Here's a nice video on how to make "bottle brush" type trees from Gutter Brushes... that are used to keep leaves out of rain gutters:
http://www.miniaturewargaming.com/index.php/mwg/comments/making_cheap_trees_from_gutter_brushes/


And here is home made flock:


http://www.youtube.com/watch?annotation_id=annotation_1233706865&feature=iv&src_vid=ntmEP46g40Q&v=5jNiiTr8Lq8


Think I'll try them out.