Temporary wallpaper: easily remove and reapply - great for apartments, dorms or for people who just don't want a long-term commitment. (Note: Target recently introduced an affordable proprietary line, nice, of removable wallpaper and coordinating paint.
Applying fabric to a wall with liquid starch is a great solution for renters and commitment-phobes alike. A bit time intensive, yes, but the results are just about as good as it gets. And unlike wallpaper, you can take it with you when you move!
10 Removable Adhesive Products All Renters Should Know About