AFAIC: as far as I'm concerned
AFK: away from keyboard
BAK: back at keyboard
BRB: be right back
IIRC: if I recall correctly
IMO: in my opinion
IMHO: in my humble opinion
IMNSHO: in my not so humble opinion
ROFL: roll on the floor laughing
ROFLMAO: roll on the floor laughing my *** off
YMMV: your mileage may vary
errr.. that's all I can think of for now, obviously waaay too much time spent on internet discussion groups