Paint, paneling. What look are you going for?
There are quite a few ways. It depends on what look you want and your budget. You can stud it out and insulate, then sheet rock. You could also use reclaimed wood for a rustic look. I've seen one cement block basement that was sealed and then painted. And I'm sure there are many other ideas. Good luck.
You need to frame out the walls with 2X4's. Insulate and cover with anything you want.
Before you put any wood product on your walls you must put a vapor barrier up first to prevent mold from forming. Wood, Moisture (dampness) and lack of air flow equals MOLD.