This article is from the Comics Misc FAQ, by with numerous contributions by FAQcis Uy firstname.lastname@example.org others.
http://www.hoboes.com maintain lists of publishers, creators, and other
comic-related addresses and URLs.
BTW, pros online should be treated the same as any other RAC'ers. It's nice
if they read or answer your posts, but they're not paid to do so any more
than you are. General compliments/fan mail should be sent by email rather
than posted. Also, it's silly to ask a specific pro questions about comics
that they aren't associated with. For example, Kurt Busiek will post about
Astro City, but not about Spawn.
Steve Lieber has written a (rough draft) Guide for Pros New to Usenet.