Copied from Wiki as a good reference for some of the not so internet savy members.
Ignore all the little # references. it was a straight copy and paste.
1337 - From the word Leet, derived from the word elite
2 - too, or to
4 - For
10q - Thank you.
A C? - AH! SI?
AAF - As A Friend
ADAD - "Another Day Another Dollar
ADIH - Another Day In Hell
ADIP - Another Day in Paradise
AEAP - As Early As Possible
AFAICR/S/T - As far as I can recall / remember / see / tell
- As far as I know
AFAP - As Far As Possible
AFK - Away from keyboard
ASAP - As soon as possible
ASL or A/S/L - Age / sex / location
ASLP or A/S/L/P - Age, sex, location, picture
ATEOTD - At The End of the Day
ATM - At the moment
AWOL - Absent Without (Official) Leave
AYBABTU (also abbreviated as AYB) - w:All your base are belong to us (from the video game Zero Wing)
B2B - Business to Business
B2C - Business to Customer
B4 - Before
BBIAB - Be back in a bit
BBQ - Barbecue. While not internet slang in itself, it is often combined with other initialisms as a point of satire, absurdity, or a non-sequitur. For example OMG WTF BBQ.
BBL/BBS - Be back later / shortly / soon
BCNU - Be seein' you
BFF - Best Friends Forever 
BFN - Bye For Now
blog - Also known as web log or an online journal
BOFH - Bastard operator from hell
bot - Any type of automated software in chatrooms and web-cataloging software
BRB - Be right back
BSOD - Blue Screen of Death
BTDT - Been there done that
BTW - By the way
bump - Increment (For example, C's ++ operator.) or a backronym for "Bring Up My Post"
CMIIW - Correct me if I'm wrong.
crawl - To retrieve a web page along with the hyperlinks that reference it
crapplet - A poorly written computer application
CU - See you (later)
CYA - See ya OR Cover Your Ass
cyber- (prefix) - A term used to connect the subsequent word loosely to the world of computers or the Internet or sex over a computer
cyberspace - Virtual reality, the Internet, the World Wide Web, and other kinds of computer systems. Science fiction author William Gibson popularized the term in his novel Neuromancer. Gibson used the word to describe a virtual world of computer networks that his cyberpunk heroes 'jacked into'
DFTT - Don't feed the trolls
DIAF - Die in a fire
DILLIGAF/D/S - Does it look like I give a flip / **** / damn / shit
DND - Do not disturb
DOA - Dead on arrival. Refers to hardware that is broken on delivery.
EOF - End of File
EOM - End of Message
EOL - End of Life. Device or hardware that is at the end of its product life cycle. - End of Line.
EQ - EverQuest
ETA - Estimated time of arrival
FAQ - Frequently Asked Question(s)
FFS - For ****'s sake
flamer - Someone who makes inflammatory, abusive or directly offensive comments. Similar to, but not quite the same as an Internet troll.
FMCDH - From My Cold Dead Hands
FOAD - **** off and die
FOAF - Friend of a friend
FTFY - Fixed that for you
FTL - For the loss
FTW - For the win
FU - **** you
FUBAR - ****ed up beyond all recognition / repair (from military slang; pronounced "foo-bar")
FUD - Fear, Uncertainty and Doubt (the purposeful spread of misinformation)
FWIW - For what it's worth
FYI - For your information
GBTW - Get back to work
GF - Great/good fight
GFU - Good for you
GFY - Go **** yourself
GG - Good game, used at or near the conclusion of a gaming match
GGS - Good games
GJ - Good job, often used in online gaming when a teammate performs an act benefitting his team, such as killing an opponent or enabling that kill
GMTA - Great minds think alike
Godwin's Law - Dictates that the longer a thread, the more likely someone will post a comparison involving Nazis or Hitler
gratz - Congratulations
GTFO - Get the **** out
GTG or G2G - 'Got to go' or 'Good to go'
GR - Good Race
HAND - have a nice day
handle - Name used in online chat, (AKA nick(name), alias, screen/user name)
HF - Have fun
haxor or H4x0r (1337) - Hacker
hit - A request made to the web server, (noun) the results of an internet search, (verb) loading a Web page. Hits are not equivalent to visitors of a webpage.
home page - The website's introduction page, starting point, and guide. The technical term is "index"
hot list - A collection of publicly available URLs (World Wide Web site addresses), sometimes available as text files.
HTH - Hope this / that helps
IANAL - I am not a lawyer
IBTL - In before the lock
IDK - I don't know
IONO - I don't know
IIRC - If I recall / remember correctly
IIUC - If I understand correctly
IMO/IMHO/IMNSHO/IMAO - In my (humble / honest / not so humble / arrogant) opinion
Information superhighway - The Internet (AKA: I-way, infobahn)
IOW - In other words
IRC - Internet Relay Chat
IRL - In real life
ITYM - I Think You Mean
IWSN - I want sex now
IYKWIM - If you know what I mean
jaggy - aliased computer graphics
JAS - Just a sec
JFTR - Just for the record
JK or j/k - Just kidding, or joke
k or kk - OK
KISS - Keep it simple stupid.
KOS - Kill on sight
KTHX - OK, thanks
KTHXBAI - OK, thanks, goodbye, used either to cut short a conversation or to express displeasure with being cut short
L8R - Later, L8R also sometimes abbreviated as L8ER is commonly used in chat rooms and other text based communications as a way of saying good bye.
lag - Slang term for slow Internet speeds or high Internet latency; Lag is sometimes due to a server problem, but more frequently due to the connection between client and server. A slow or intermittent connection may often be referred to as laggy
lamer - A know-nothing, one who is lame.
leet - Often spelled as l33t or 1337. It originally meant elite
LFG - Looking for group
LFM - Looking for more
LMAO - Laughing my ass off
LMFAO - Laughing my ****ing ass off
LMIRL - Let's meet in real life.
LMK - Let me know
LOL - Laughing out loud, laugh out loud
LTNS - Long time no see
lulz - corruption of LOL
lurker - Someone who frequents a Usenet group without participating in discussions
LYLAB - Love you like a brother.
LYLAS - Love you like a sister.
MMORPG, MMO - Massive Multi-player Online Role Playing Game
MOTD - Message of the day
MTFBWY - May The Force be with you 
MUD - Multi-User Dungeon
MUSH - Multi-User Shared Hallucination
MYOB - Mind your own business
M8 - Mate
N1 - Nice one, used mostly often in gaming
NE1 - "Anyone"
newbie, newb, n00b - An inexperienced user of a system or game, or an annoying person. Usually a derogatory term for someone inexperienced at a game.
NIFOC - Naked In Front Of Computer
NM - (Sometimes written N/M) Not much, Never mind or no message, used on message boards or in e-mails to indicate that everything is already said in the subject line.
NP - No problem
NSFW - Not safe for work. Warning about content that may get the viewer in trouble with his employer or co-workers.
NVM, NVMD, or nm - Nevermind, not much
O RLY - Oh really?
OIC - Oh, I see
OFN - Old freaking news
OMG - Oh my god
OMFG - Oh my ****ing god
OMGWTF - Oh my God what the ****/>
OMW - On my way or Oh my word
ONOZ - Oh, no
OP - Original poster / Operator / Outpost
OS - Operating system
OT - Off topic
OTOH - On the other hand
OTP - On the phone or One true pairing or On The Piss
P2P - Peer to peer, or pay to play
PAW - Parents are watching
PEBKAC/PEBCAK - Problem exists between keyboard and chair
ping - From the popular network monitoring tool.
PITA - Pain in the arse / ass
PLMK - Please let me know
PMSL - Pissing myself laughing
POS - Piece of shit, or parent over shoulder.
POTS - Plain old telephone service
POV - Point of view
PL - Powerleveling, used in online games.
PPL - People
PTKFGS - Punch the Keys For God's Sake
pr0n - Intentional misspelling of porn
PW - Persistent World (gaming)
pwned - Intentional misspelling of owned
QFT - Quoted for truthiness - either to show satire or agreement with something satiric.
QWP - (texting) Quit Whining, Please. (gaming) equip v / equipment n.
rehi (or merely re) - Hello again
RL - Real Life
RMS - Ride me sideways
ROFL/ROTFL - Rolling on (the) floor laughing
ROFLMAO/ROTFLMAO - Rolling on (the) floor laughing my ass off
ROFLMAOWPIMP/ROTFLMAOWPIMP - Rolling on (the) floor laughing my ass off while peeing in my pants 
ROFLOL/ROTFLOL - Rolling on (the) floor laughing out loud
RSN - Real soon now (used sarcastically)
RTFB - Read the ****ing binary (or book)
RTFS - Read the ****ing source
RTFM/RTM - Read the (****ing) manual or reboot the (****ing) machine
SCNR - Sorry, could not resist
SFW - Safe for Work, see NSFW
sk8/sk8r/sk8er - skate/skater
smiley - Another name for emoticons
SMH - Shaking my head
SNAFU - Situation normal: all (****ed/fouled) up
Snail mail - Normal paper mail service
SOHF - Sense of humor failure
spider - The program behind a search engine
STFU - Shut the **** up
STFW - Search the ****ing web
TANSTAAFL - There ain't no such thing as a free lunch, a quote originally attributed to Robert Heinlein
TBF - Time between failures
TBH - To be honest
TG - That's great
TGIF - Thank God it's Friday
THX/THNX, TNX or TX - Thanks
TIA - Thanks in advance
TINC - There Is No Cabal, a term discouraging conspiracy theories
TMI - Too much information
TOOBS - Internets (refering to the internet as a series of tubes)
TOS - Terms of service
TTBOMK - To the best of my knowledge
TTFN - Ta ta for now
TTYL - Talk to you later (also spelled TTUL, T2UL or T2YL)
tweedler - One who has deep love for all computer related technology and gadgets
TY - Thank you 
TYT - Take your time
TYVM - Thank you very much
U - You
UTFSE - Use the ****ing search engine
w00t, w00T or WOOT - First two express exuberance, the last is a backronym for the term "We Own the Other Team".
W/ or W/O - With or without
WB - Welcome back
W/E - Whatever
WRT - With respect / regard to
WTB - Want to buy
WTF - What the ****
WTG - Way to go
WTH - What the hell
WTS - Want to sell
WTT - Want to trade
WUG - What you got?
WUBU2 - What (have) you been up to?
WUU2 - What (are) you up to?
WYSIWYG - What you see is what you get
W8 - Wait
YHBT - You have been trolled.
YKW - You know what?
YMMV - Your mileage may vary.
YTMND - You're The Man Now, Dog
YW - You're welcome.
YOYO - You're On Your Own.
YAGTOH - you are going to own him.
ZOMG - An intentional misspelling of the acronym shorthand for "Oh My Gawd" and pronounced "Zoh My Gawd" This version is mainly used in jest or to ridicule people who use abbreviations like OMG and OMFG