Trees!
Consider creating an interesting silhouette and realistic textures for your tree. Keep the modeling simple under 1000 polygons. Don't try to model every leaf and branch consider how you can use transparency maps and single sided geometry to create a mass of leaves with little modeling.
What is the enviroment for your tree? Is it a landscaping tree, a forest tree or something completely alien? All trees have roots, leaves and a forking branch pattern we should be able to see that in your model.
Got reference? Get started here:
http://flickr.com/search/advanced/
google image search
Take a look at this the visdev tree challenge on...
http://creationengines.blogspot.com/
