A while back I finally found some time to start learning GrowFX and it's been a lot of fun! I highly recommend looking at it if you're looking to make your own vegetaion for your scenes.
The models I've been making with lately are starting to shape up quite nicely. As I'm still just experimenting I decided to share some of my creations. The first of these is a pack of 10 "generic" trees. They haven't been modeled after any particular species, but if you need quickly some models to populate your scene these could work out for you.
The render below was made with the tree pack and Grass Generator, using textures found at CGTextures.com. All the trees are in OBJ format, no textures are included. The pack is about 1.2 GB to download.
As you can see from the screenshot to the left, all of the models include roots. The Material ID's and UV are also prepared for easy texturing.
Material ID's 1 through 5 are for the roots, trunk, branches and twigs, ID's 6 through 8 are for the leaves.