Ryan Smith, aka Virtuosic, has released a free beta of TreeGen, his tree-generation script for 3ds Max.
Although not as complex as commercial tree-generation software, TreeGen provides users with over 35 parameters for controlling trunk, branch and leaf shape; and the option to apply custom bark materials.
Roots are coming in a future release, according to Smith, by day a FX artist at id Software.
Read the TreeGen release thread on Polycount
(Includes download link.)
Hat tip to Max Underground for spotting this one.