Every home I've ever owned with a basement, I notice a marked amount of humidity in the basement compared to the upper floors. I think it's because the basement (concrete, cinder block) walls are in direct contact with the soil (newer homes usually have a barrier or membrane fastened to the outside walls, which keeps water away from the wall, and forces it down to the footings, where the weeping or drainage tile is located), which contains a fair amount of water. If you don't have moisture on the floor, or coming through your walls, a de-humidifier might do the trick in reducing the amount of humidity in the air. I've found it dries out the basement immensely and instead of being cool and damp, you'll find it warm(er) and dry. (I like a cool basement, however, especially in summer, as it's nice to go down there on a hot day.)
I've just recently dug up my own basement. Water problems coming in through floor on west side of house. Trenched along the problem wall, installed drainage tile (perforated pipe) beside the footing, and run it (tile) to sump pit in basement. Am hoping this reduces the amount of water I get on the west side of my house (in basement). Shortly after I got the trench dug on the problem side of house, water began to permeate the soil, and filled up the trench. I got 4 - 6" of water in the trench. This shows you how much water can accumulate around and under your foundation.
