Some very basic and commonly used forum lingo are listed below:

AFAIK - As far as I know
BTW - By the way
FWIW - For What it's worth
FYI - For your information
IIRC- If I recall correctly
IMHO - In my humble opinion
IMO - In my opinion
LMAO - Laughing my @$$ off
LOL - Laugh out loud
OTOH - On the other hand
ROTFLOL - Rolling on the floor laughing out loud
ROTFLMAO - Rolling on the floor laughing my ass off
RTFM - Read the F-ing Manual
YMMV - Your methods/mileage may vary