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.
If you like post apocalyptic landscapes of Crysis 3 and Enslaved, you should definitely check this guy out. The designer by the name of Ainas from Lithuania (creator of BF2 Spec Ops Warfare MOD) creates fantastic scenes of utter destruction that look like images out of a very sad fairy tale.
These environments were carefully constructed in CryEngine. They look very nice, but seem to lack some details. You can’t argue that his design is very atmospheric and enjoyable.
I got inspired by The Last of Us, Crysis 3 and Survarium. I mixed a lot of design techniques and got pretty nice result. Also this level is totally improv. I had no actual concept or art. It was design just in process. I was responsible not only for terrain, level design but for assets too. I made custom textures for custom assets (models are not mine).