I love World Creator, especially the vegetation distribution pipeline. You can create some very realistic fields with it. Im going to check out impostors too - ive seen it a few times and wondered what it's about.
Stupid Rental. My Zbrush that I haven't paid for an update in years and is perpetual Trumps that on all counts.
Better Level Design Through Human Survival Instincts (Christopher Totten) 3/6
The third part of the talk Christopher Totten talks about the issues of light and darkness, heights and covers in videogame design and gives his opinion on the subjects.