BTW By the way
IMHO In my humble opinion
IMNSHO In my not so humble opinion
IOW In other words
IRL In real life
ITRW In the real world
LOL Laughing out loud
MorF? Male or Female? (used in chat areas for people with gender-neutral handles)
OTF On the floor (laughing)
ROTFL Rolling on the floor laughing
RTFM Read the f***ing manual (said in response to a stupid question)
WRT With regard to
YMMV Your mileage may vary
<g> or <G> Grin
<bg> Big grin