If you are looking for rock formations, hankster has a couple of nice sets in the marketplace. I agree, for trees and shrubs RDNA has some of the best selection and quality. Check LisaB's offerings at Daz for flowers. Free flowers at planit-3d. I've been using Bryce to make specialty terrains and inporting them into Poser. By applying magnets some very alien landscapes can be created.

I must remember to remember what it was I had to remember.