I once tried to get involved on RetroJunk, but I can't seem to like most people on that site.
I'm currently active on Toon Zone and DK Universe, and I'm registered at Rangerboard and Wrestlecrap, though I haven't posted on those two places in a long time. I also lurk GameFAQs, Advance Wars Nation, and Something Awful, mainly for the rampant stupidity in each of those places.
I avoid Serebiiboards and anything Sonic related like the plague.