FYI:
IMHO: In My Humble Opinion (i.e. this is just my opinion)
IMNSHO: In My Not-So-Humble Opinion
YMMV: Your Mileage May Vary (i.e. this works for me, but might not for you)
BTW: By The Way
FYI: For Your Information
F'ex: For example (e.g.)
RL: Real-Life
IC: In Character [referring to roleplaying]
LOL: Laughs Out Loud
ROTFL: Rolls On The Floor Laughing
{g}: {grin} -- Another system of expressing emotion involves abbreviations
like this...
{g,d,r}:{grin, duck and run}