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.
HDR Light Studio 4
A video presentation showcasing features of the HDR Light Studio 4 software. It shows how HDR Light Studio helps with dynamic HDRI map. It allowed to create and control image based lighting.