EDIT: The free content at vyonyx has been moved to http://www.gobotree.com/
Are you getting tired of using the same RPC people and trees in all your Revit renders? Maybe you should try adding some of these free trees and people in your render post-editing program (such as Photoshop):
From their Disclaimer: All the contents in our download section are absolutely free of any charge and there is no limitation on their personal or commercial use! …
Along similar lines, I previously posted about Immediate Entourage here.