Awesome forum, by the way. Very informative. Lotsa great info.
I am a bluegrass fanatic, and really enjoy the various rhythm styes used by various artists. Youtube has some awesome instructional vids. Wyatt Rice has a few great vids on youtube. He's fantastic. He's got his rhythm down to a fine art. Hope it's okay to post vid links on Guitarnoise. Here's one:
Another (if you can take your eyes off of Grier's pickin'): http://www.youtube.com/watch?v=IgfKZRujgbs
with Tony Rice: http://www.youtube.com/watch?v=Z5VayE24CFI
Also, Brad Davis is awesome. Here's a good vid:
I recently purchased Orrin Star's Bluegrass Rhythm Guitar Workshop, and I think it's excellent. While play...er, practice...bluegrass stuff, most of my friends play other stuff. From this, I've noticed that the rhythm techniques I've learned fit well into most genres.
These two are your best bet. Keller plays the best acoustic stuff that I have ever heard. Do a youtube search.