A worldwide community photographing and learning about wildlife
Pin oak
I haven't used the app, but it sounded interesting. Sounds that they still have some work to do on it....
If you are using a smart phone, you might want to consider a free app called Leafsnap. You take photo of a leaf against a white background and it analyzes the leaf shape and tells you the likely species. I think it's only available right now for trees in the northeast US. It's interesting technology.