AFAIK As Far As I Know
AFK Away From Keyboard
ASAP As Soon As Possible
ATK At The Keyboard
ATM At The Moment
A3 Anytime, Anywhere, Anyplace
BAK Back At Keyboard
BBL Be Back Later
BBS Be Back Soon
BFN/B4N Bye For Now
BRB Be Right Back
BRT Be Right There
BTW By The Way...