DW (Dark Wolves, the first clan I was ever in)
SSB (my guess is Super Smash Brothers :P).. although that makes sense because Link and Kirby are in it...
MERC (Mercenaries - now just the roots through many merges of DM - Dark Mercenaries - which was also the roots of EM, which Tublear listed)
KR (the beginning of my name, which a lot of people used to think/still think is/was a clan)