For gaming forums I only tend to post here, though I sign up for membership at every site I visit, just in case I feel the need to post there. I visit gametrailers every week or so for the latest AVGN videos and Screwattack top tens, which in turn led me to sign up for ScrewAttack which I visit 2-3 times a week.
I visit Kotaku daily because they usually do a good job of finding and posting all the worthwhile news and rumours which saves me the effort of doing it myself.
I also visit XBox.com solely to check out my achievements or check release dates, and Bungie.net to track my matchmaking stats, though I occasionally browse the Halo 3 forums there too.