I am obsessed with wall graphics. Mostly for baby rooms or play rooms. But even in living rooms or hallways, too. I recently purchased the above boodalee tree wall graphics for my son's room and it looks awesome. It wasn't the easiest thing to put up, but at least It's better than buying a bunch of paint and trying to do it yourself! They are removeable, so you don't have to worry about ruining paint or painting over the decals when you want to redecorate the room.
Other Decal Designers:
Wonderful Graphiti - custom decals and other premade quotes and words
artdeco - a wide variety of of sports and nature designs
Blik - you can pretty much find everything here, all designers and custom options