Wallpaper right now.
If it weren't such a commitment I would definitely do wallpaper in at least one of my rooms.
I particularly like it when just one wall is featured in wallpaper and the rest are painted a complementing solid like this room via Apartment Therapy.
Ughhh I just don't know if I can depend on myself not to get tired of it...
But here are some cute patterns I like from good, old, dependable Target.
(The Lime Green is my fav)