How about african zoo theme like giraffes and elephants and lions zebras you could get wall decals of the animals, or cheery blossems in a girls room, Disney movie themes are always cute so is an airplane themed room with an actual wooden aorplane hanging from the ceiling and underwater theme with fishes and whales on the walls.
I think a nursery is a like a pair of shoes, you have to be absolutely in love with it! Thats how I pick out all my stuff. You might have to browse a few times for a few different themes but once you find the one you'll know!
I have my one year old who is going to share with her new baby sister, and we put her new toddler bed and the crib in the room, and I I really like the minnie and mickey mouse theme! Plus Daisy is a minnie mouse nut....LOL