Heh, I'm in a sharing mode today...plus having a cute RO avatar helps! ^_^
http://bbs.greedland.net/ - Quality group. My favorite site for Death Note! Prince of Tennis, Death Note, Black Cat, Naruto, Shaman King, Hunter x Hunter
http://www.fycomic.com/ - Quality group. Does similar series as GreedLand, it's the only group that does D.GrayMan
http://jojohot.com/ - Fastest and most popular speed-scanslation group but usually in simplified Chinese. Many many popular series (Ah! My Goddess, Naruto, Full Metal Alchemist, Bleach, EyeShield 21, Death Note, Midori no Hibi, GANTZ, Tenjou Tenge, etc), but the site is kinda annoying to navigate and they only serve the three most recent chapters. The forum is quite active and nice, though
http://www.manlu.com/ - Serves some of the most popular JOJOHOT series (it's often down on Fridays and Saturdays)
http://miyusky.com/bbs - HIGH-quality group. Often in simplified Chinese. Mainly do Tsubasa, xxxHolic, and Fruits Basket. Also does Magister Negi Magi I think, but I don't like theirs that much.
http://www.howgame.com/bbs/ - HIGH-quality group. Formerly Final Eden/Aya vs Tsukasa, this is the place to get the latest Ichigo 100%!