Shelving: If you've got room, add some shelving just make sure to anchor them well and to anchor what's on them so they don't shake off in an earthquake. This is harder to undo when you move, but could be well worth it if you need more storage or to break up a lot of wall.
Add Temporary Wallpaper: they are normally vinyl based so that they can peel off more easily later so that solves some of the moisture issues and, as stated by a reader, they peel off without a trace when you're all done. (check out
Tile decals can be added to liven up some ho hum tile without any real work or committment. Just peel them off when you get tired of them.
Use Painted Pegboard to add organization and color to your backsplash. Just make sure to use glossy paint! Have it cut in sections to fit and then either drill (if you can) or affix with some crazy foam tape or braces that come down from the upper cabinets.
Paint a Bright Color if you don't have tile then you can paint the backsplash any color you want and paint it back when you move. Laura painted hers turquoise, ours is a light blue and Maxwell and Sara Kate's is a warm yellow. What color is yours?