Here's where to find all your favorite riffers online:

Cinematic Titanic:
Trace Beaulieu: Facebook and Twitter
Frank Conniff: Facebook, Twitter, MySpace (he's the Frank of All Media)
Mary Jo Pehl: Facebook
J. Elvis Weinstein: Twitter
Joel Hodgson: on Facebook, sure, but doesn't friend fans, to my knowledge.

Rifftrax:
Mike Nelson: on Twitter and MySpace
Kevin Murphy: Facebook and Twitter
Bill Corbett: Facebook and Twitter
Conor Lastowka: Facebook and Twitter

And both Titans and Rifftones blog on their respective sites.