Here's some of the common ones, there are thousands more
AAMOF as a matter of fact
BBFN bye bye for now
BFN bye for now
BTW by the way
BYKT but you knew that
CMIIW correct me if I'm wrong
EOL end of lecture
FAQ frequently asked question(s)
FITB fill in the blank
FWIW for what it's worth
FYI for your information
HTH hope this helps
IAC in any case
IAE in any event
IMCO in my considered opinion
IMHO in my humble opinion
IMNSHO in my not so humble opinion
IMO in my opinion
IOW in other words
LOL lots of luck or laughing out loud
MGB may God bless
MHOTY my hat's off to you
NRN no reply necessary
OIC oh, I see
OTOH on the other hand
RCH red c*** hair(unit of measure)
ROF rolling on the floor
ROFL rolling on the floor laughing
ROTFL rolling on the floor laughing
RSN real soon now
SITD still in the dark
TIA thanks in advance
TIC tongue in cheek
TTYL talk to you later
TYVM thank you very much
WYSIWYG what you see is what you get
YKYBNTLWYKT you know you've been on the net too long when you know all these
There are some acronyms that have different meanings depending on the field they are used such as TPS
Throttle Position Sensor
Technical Publication Software
Technical Publishing Software
Teleprocessing Services
Thermal Protection System
Trailer Park Slattern
Transaction Processing System
Transactions Per Second
Go here
http://www3.sympatico.ca/dhaughey/ for ones used in automotive lingo