This is not new info or anything, so if you already know how to get feeds from vB forums then you can ignore this entry.
I am registered at a fairly large number of forums, I only actively monitor a few of them, which ones of them depends on what I’m into or what I’m looking into buying. 😉 A majority of these Internet forums are powered by vBulletin, and IIRC, RSS feed is enabled by default. Most owners of these forums don’t provide links or advertise the fact that these feeds are enabled, probably because they don’t know about this feature (and Feedburner), or they have board sponsors and assume when people come in via feeds it would bypass their ads. Anyway, since RSS is enabled on most of these boards, here is how you can get to them:
If the URL of the site looks like http://forums.foo.com, the feed for the entire site should look like http://forums.foo.com/external.php?type=rss2 (use just “rss” if you want RSS 0.91).
You can also get the feed for a particular forum, go to the forum you want and note the forum ID, if the end of the URL looks like forumdisplay.php?f=23 then the ID is 23. The feed for that forum is http://forums.foo.com/external.php?type=rss2&forumids=23