http://www.anapsid.org/internet/smileys.html#abbrev (FriarJohn's Link) 
TTBOMK (to the best of my knowledge)
TANSTASQ (there ain't no such thing as a stupid question).
SOW (speaking of which),
YGLT (you're gonna love this ),
OTTOMH (off the top of my head),
NTYMI (now that you mention it),
IMHO (in my humble opinion),
TCGOFE (this could go on for ever).
AFAIC (as far as I'm concerned), it's
TEOTWAWKI (the end of the world as we know it).
ROTFLOLSTC (rolling on the floor, laughing out loud - scared the cat!),
Soren
