Here are some ideas from another forum I post upon:
:: go buy huge sheets of interesting fabric. pin them tightly on the walls at the baseboard and the ceiling. fold the egdes under before you pin for a nice, clean look. VOILA! faux-wallpapered walls. (Sari fabric works great for this, it's gorgeous, relatively inexpensive, and comes in huge peices.)
:: Urban Outfitters does some gaudy as all hell murals, as does Home Depot. Who doesn't want to sit in their living room and feel like they are hovering over the Strip? Yikes
:: Other alternatives: buying cheap canvases from Michael's craft store and painting them in solid colors to hang in a square shape. Something I've considered doing is cutting decals out of cling material to stick to a wall. Not unlike this:
:: use starch to apply fabric to your wall like wallpaper! you can put whatever you want on the wall, and when you need to move (or change your mind about your walls), just pull it down, wash the wall, and its just like it was before you started! Link to more in depth instructions
here
:: floating shelves from IKEA or Home Depot, arranged in a 'stair' pattern to fill up wall space
