The following is a short list of both Emoticons and Acronyms commonly used on the Internet. There’s a lot more than this (some nice, some not) and if you’re interested in finding out more, do a search on Google for emoticons. [:)]
Here are additional reference for more acronyms:
Internet Abbreviations
Internet Acronyms Dictionary
Emoticons
Emoticons (emotional icons) are used to compensate for the inability to convey voice inflections, facial expressions, and bodily gestures in written communication. Some emoticons are better known as “smileys.” Emoticons can be very effective toward avoiding misinterpretation of the writer’s intents. While there are no standard definitions for the following emoticons, we have supplied their most usual meanings. Most emoticons will look like a face (eyes, nose, and mouth) when rotated 90 degree clockwise.
or Expresses happiness, sarcasm, or joke
or Expresses unhappiness
:] or :-] Expresses jovial happiness
:[ or :-[ Expresses despondent unhappiness
or Expresses jovial happiness
:I or :-I Expresses indifference
:-/ or :-\ Indicates undicided, confused, or skeptical. Also 
or :.
:Q or :-Q Expresses confusion
:S or :-S Expresses incoherence or loss of words
:@ or :-@ Expresses shock or screaming
or Indicates surprise, yelling or realization of an error (“uh oh!”)
Acronyms
AAMOF As A Matter Of Fact
AFAIK As Far As I Know
BBFN bye bye for now
BFN bye for now
BTW by the way
DITW Dead In The Water
DYOH Do Your Own Homework
EOL end of lecture
FAQ frequently asked question(s)
FITB fill in the blank
FUD Fear, Uncertainty, Doubt
FWIW for what it’s worth
FX Effects
FYI for your information
GBFN Good-Bye For Now
HTH hope this helps
HTML - Hyper Text Markup Language
IAC in any case
IAE in any event
IANAL I Am Not A Lawyer
ICBW I Could Be Wrong
IIRC If I Remember/Recall Correctly
IMCO in my considered opinion
IMHO in my humble (or honest) opinion
IMNSHO in my not so humble opinion
IMO in my opinion
IOW in other words
IRL In Real Life
LOL lots of luck or laughing out loud
MHOTY my hat’s off to you
NRN no reply necessary
OIC oh, I see
OTOH on the other hand
ROF rolling on the floor
ROFL rolling on the floor laughing
ROTFL rolling on the floor laughing
SIG Signature
SITD still in the dark
TIA thanks in advance
TTFN Ta-Taa For Now
TTYL talk to you later
WYSIWYG what you see is what you get
YMMV Your Mileage May Vary
Grinning
Joking
Laughing
Smiling
Yawning
Additional Acronyms Commonly used in Forums/Newsgroups
AUCTION - Items for Auction
FA - Items for Auction
FS - Items for Sale
FT - Items for Trade
ISO - In Search Of
WTB - Want to Buy
WTD - Want to Deal (buy or trade)
WTS - Want to Sell
WTT - Want to Trade
OT - Off-Topic
…of course there are a lot more.