Here is another basement that has been fixed up to have more "livable space" for little money. The concrete walls have been painted and furniture and area rugs added. Throw in a game table and for very little money you have a place for the kids to play with the noise a floor away. Buyers will see more value in the home.
In this basement they used a warm, sunny color on the concrete walls. Then added some artwork and some furniture to make it feel homey. One thing to keep in mind, though, when doing a bedroom in the basement, it needs a fire escape window to make it legal and safe. Check with you local building codes to be sure you are in compliance.