The ultimate on-line knife discussion forum. Everyone who is anyone hangs out on bladeforums.com You'll find me there all the time. Be sure to check out the new balisong forum. which Clay and I help moderate.
Another good knife discussion forum you'll find me on. Be sure to check out the new Big Steak and Single-Malt Scotch forum, which I moderate, a forum about knife enthusiast's other excesses.
Yet another forum site. This one is primarily about custom knives and a lot of the discussion is about the technical details of making knives. I haven't seen much about balisongs here. I don't read this one often and am not a member, not because I don't think it's a fine site, but just because there's only so much time in the day.
Benchmade has recently added a new section to their forums section just for balisongs. (They also win the prize for biggest logo.)