Need ideas - DS nursery walls?

DS's nursery is rather gender neutral so far...I don't like traditional boy stuff. But I don't know what to put on the walls. Prints, but of what? Any ideas or ideas of where to start looking?

The color scheme is mainly green, dark chocolate, and white.

 With those colors, I'd probably do nature-y type things. Maybe vinyl wall art/mural of a big tree. Maybe even some b/w framed photos of natural elements.

 We have pale yellow/cream colored walls in our DS's nursery, and we accented in sage green, dark brown and khaki.  We did a safari theme.  We got prints to match our crib set and they are images of animals from our bedding: a lion, a monkey and a crocodile. I also made letters of his name and a separate piece of wall art with all of the animals from our bedding. It turned out really cute, let me see if I can figure out how to post images, I am really proud of it :)

 I did my ds's nursery in blue jean teddy. It was cheap and they have wall stickers that are static cling. They actually stick extremely well and come right off when you need them too. Here are some pics of their nusery: