The spoonflower blog had a series called Rental Dec - which had a whole series of removable projects with wallpaper and decals designed for renters.

"Renters, rejoice! For the month of May, we're sharing DIY projects to personalize those temporary spaces we call home. We're bringing you simple and beautiful how-tos easily achieved with custom removable wallpaper and decals"

Will PM you the link. It gave me some ideas, we are not renting - but wanted some non-permanent ideas.