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):
Cutout People | VYONYX
Cutout Trees | VYONYX
Along similar lines, I previously posted about Immediate Entourage here.
vyonyx also host:
Textures | VYONYX
References | VYONYX (think water, grass, backgrounds etc)