No foolproof cure exists for wet basements, despite what a  salesperson or home improvement contractor may promise.
A homeowner who takes the time to become thoroughly familiar with the full range of possible causes and potential remedies will be far more likely to obtain effective and lasting repairs than one who settles for the first, easiest, or least expensive method proposed as a solution.
This may turn out to cost you more.

LOOK FOR OBVIOUS SOLUTIONS
The cause of a wet or damp basement can be minor, readily apparent, and easily corrected. Here are some possible solutions. For example: 
Problem: The source of water in the basement is a mystery

Solution: To determine whether the water is seeping in from the outside or condensing inside, tape a twelve-inch square of aluminum foil to a wall that is prone to dampness, sealing all four sides to make the surface behind the foil as airtight as possible. In a day or two, if the side of the foil that was against the wall is wet, the problem is seepage. If the outside is wet, it's condensation

Problem: Lawns that are flat or slope toward the house permit surface water (rain and melting snow) to drain down against basement walls. Water enters through cracks or other openings in the walls and causes wet spots on the walls or standing water on the floor.

Solution: Slope the ground away from the outside foundation (should be about one inch per foot). Extend the slope for at least ten feet. Seed it with a good lawn grass. Sodding is a common practice and prevents the washing away of newly graded areas during heavy rains. Where a large area of land slopes toward the house, surface drainage should be intercepted and rerouted some distance from the house. Dig a shallow, half-round drainage ditch or depression designed to route the water around the house. Sod the ditch or plant grass in it. If even a shallow ditch is objectionable, drainage tiles, with one or more catch basins at low spots, may be installed. See this Drawing

Problem: Defective, clogged, or nonexistent gutters and downspout's allow roof water to form puddles or wet soil near or against basement walls, and enter through cracks or openings in the masonry.

Solution: Install gutters and downspout's wherever needed. Keep them free of debris. Where leaves and twigs from nearby trees may collect in a gutter, install a basket-shaped wire strainer over the downspout outlet or place screening across the length of the gutter. Repair gutters and downspout's as soon as the need appears. To prevent concentration of water at the point of discharge, use a concrete gutter or splash block to carry the water away at a slope of one inch per foot. Roof water can also be piped underground to a storm drain, dry well, or surface outlet fifteen feet or more from the house
How To Build and install splash blocks and dry wells

Problem: Dense shrubbery and other plantings around the basement walls prevent good ventilation.

Solution: Trim heavy growths of shrubbery so that soil gets more sunlight and dries quicker. When digging up the plantings, remove any pieces of masonry, mortar, or other waste material buried near the house after the basement was excavated.

Problem: Unprotected basement window wells act like cisterns during heavy storms, permitting water to seep in around window frames and below windows.

Solution: Windows or parts of windows below grade should be protected by metal or masonry window wells, with bottoms consisting of gravel to permit good drainage. Clear plastic bubbles are available to cover the entire window well like an awning.

Problem: Atmospheric moisture produces condensation ("sweating") on cool surfaces in the basement, particularly walls, floors, and cold water pipes. Solution: Insulate the water pipes. Promote good ventilation--sunlight and free movement of air can quickly dry out a basement. Ventilation should be governed by weather conditions. During hot, humid weather or long rainy spells, windows should be closed because the outside air will probably contain more moisture than the basement air. Heat the basement during the winter. During hot weather, use air conditioning to cool and dehumidify the air.

Problem: Leaky plumbing or other sources of moisture--such as clothes hung to dry on basement lines--increase humidity in the air, increasing the likelihood of condensation.

Solution: Repair plumbing promptly, open windows or dry clothes in an automatic dryer vented outdoors. If the problem persists, experiment with using a large-capacity dehumidifier to eliminate condensation. (Try to borrow one from a friend or neighbor before investing in what may turn out to be the wrong remedy.)
 

CONCENTRATE ON THE SOURCE OF PERSISTENT PROBLEMS
If every apparent, logical way of eliminating wetness fails to produce a dry basement, don't waste time or money on random potential solutions. Finding the cause of the problem is absolutely essential to its cure.
Make sure the contractor takes the proper test borings of the soil. 

The hardest type of water problem to correct is one created by faulty construction practices at the time the house was built.
Proper drainage is a crucial consideration in selecting the site for a new house. This includes not only the drainage of surface water but also drainage of any subsurface or ground water that may already be present or that may accumulate over a period of time and be blocked from its normal course of flow by the new construction. If the subsurface or ground water level is close to the underside of the basement floor slab, water rises through the slab by capillary action, producing dampness.
If the subsurface or ground water level is higher than the basement floor, water leaks in through the walls and floor or enters by capillary action, causing standing water in the basement and, at times, dampness in the rooms above.

Under ideal conditions, a house should be situated so that even during rainy seasons the subsurface or ground water level is at least ten feet below the finished grade--well below the average basement floor.
In some cases it is impossible to completely eliminate dampness from a basement where the contractor did not take into consideration the basic principles of good drainage.
Only after soil borings have been done can anyone knowledgeably predict which, if any, course of action has a chance for success.

WEIGH ALTERNATIVE METHODS OF TREATMENT
An accurate diagnosis of the main cause of persistent basement wetness may lead to a recommendation of one or more of the following actions: 
Installation of a Sump Pump.
Where gravity drainage is impossible or impaired, a sump pump may be used to raise the water to a level where it can be carried off through a drain line. This type of pump is a small, simple, compact unit installed in a sump, or pit, at the low corner or other wet spot in the basement. The pit should be lined with drain tile, concrete or metal to prevent caving in of the sides. Inlets, or holes, must be provided in the lining material to admit ground water. A sump pump is designed for automatic operation. If correctly installed and not abused, it would require very little attention. Dirt, lint, trash, and other waste can clog the strainer and should be kept out of the pit.

Application of Waterproofing Compounds to the Interior Walls.
Only in cases where mild and occasional capillary seepage occurs are applications of waterproofing paint or other interior compounds likely to provide any lasting degree of improvement in achieving a dry basement. Do-it-yourselfers should carefully read the label to determine the waterproofing product's limitations and the terms of any guarantee promised.
DryLock has an excellent step by step tutorial on this Including a Video!
Please keep in mind, interior wall treatment will not work if major exterior water conditions exist.

Exterior Injection of Waterproofing Substances.
This type of treatment does not require excavation. Instead, sodium bentonite or another substance--sold under a variety of trade names--is injected into the space between the soil mass and the basement wall. It swells to many times its dry volume when it is first put into slurry form. The slurry will tend to penetrate and plug cracks where water might also find a path to the basement interior, thus reducing the flow of water. The type of soil and the skill of the person directing or performing the injection operation has a strong bearing on the success of this method to correct basement wetness. Certain chemicals, such as salt, will tend to prevent the effectiveness of the sodium bentonite, and undetected underground barriers (such as rock or wood) can seriously impair the effective use of this method. In very pervious, coarse sand to gravel soils, the soil itself can be injected with bentonite slurry, but it may not be possible to inject bentonite slurry into clay soils, silt soils or sandy soils where the sand is of fine to medium gradation.

The injection of sodium bentonite slurry beneath a basement floor might result under certain circumstances in the floor being raised by hydrostatic pressure, and tend to plug any drain tile that might exist under the floor.

The U.S. Department of Housing and Urban Development states in its Manual of Acceptable Practices for properties under consideration for FHA loan guaranties that "Pressure injected waterproofing has not demonstrated a satisfactory performance and is not acceptable under HUD standards."

Excavation.
Sometimes it is necessary to resort to the extreme measure of exposing the basement walls, treating them to make them watertight, and then regrading the soil.
 

Among possible treatments are: 
Covering the walls with a prepared waterproofing felt or fabric coated and cemented together with hot coal-tar pitch. If properly applied, the membrane is a very effective method of waterproofing. However, it is very expensive, and if subsequent leaks develop they may be difficult to locate and repair. Remember, water can still come in through the basement floor.

Application of two coats of portland cement mortar to the surface of the exterior walls. Called parging, this work should be done only in dry, mild weather. Fall is the best time, because the subsurface water level is usually low and temperatures are more favorable for making watertight concrete. The newly cemented walls should be properly protected and cured. Freezing or rapid drying of the concrete by sun or wind can damage it and make it worthless. In very wet soils, the parged wall surfaces may be given two coats of hot coal-tar pitch. Keep in mind that settlement and thermal expansion and contraction of the wall can affect the parging; the coating, therefore, is important. Look into cement additives where you buy your materials. They now make polymer (waterbase) additives that give concrete and cement mixes terrific bonding power and flexibility.

Application of polyethylene or polyvinyl film, a vapor barrier material, to the exterior surface of the walls. Manufacturers' instructions should be followed in applying the material.

Installation of draintile around the footings, at least on the sides where trouble is occurring. This procedure is generally recommended in addition to one or more methods above. Good, four-inch drain tile should be used, laid parallel with, and at the bottom of the footing. Great care must be taken to see that the bottom of the tile is not lower than the bottom of the footings, so that the footings are not undermined. In normal, porous soil, the tile should be covered with 18 inches of screened gravel. In heavy, non-porous soil, the gravel should extend almost to the top of the excavation. This footing drain and belt of gravel should drain off all seepage water and prevent the accumulation of water around the walls. This method is especially suitable on the upper side of a house located on a hillside.

Once you have a nice dry basement, keep the heat in during the winter, out during the summer, and stop condensation with "Radiant Barrier Coat" a reflective water vapor blocking wall and ceiling latex paint.