Superb list there.
I was going to mention that Dosch also sells plants, though since they sell on their own as well as broker through TurboSquid, buying direct probably won't save much money. I think the site is DoschDesign or something like that.
Often times, for the long-term, you will save money buying something like Xfrog or Onyx/TreePro. Initial investment is high, but for lots of work it will pay off eventually. Depends on your situation - in mine, Tree Pro has paid for itself many times over... and Onyx's newest offerings include flowers and stuff as well. Can't compare to Xfrog's package, but from what I've seen firsthand, the Onyx software learning curve is non-existent and their generated trees and flowers are absolutely top of the line, better than what I've seen from Xfrog though that might have been just the guy who was using it didn't know how to get optimal results. I know the Xfrog package will ultimately do more stuff, but at the cost of a much steeper learning curve. Onyx's stuff is practically drag-and-drop, with very high fine controls but only if you want them.
Just another $.02...
