I thought since we're collecting all these, I might as well start a topic that combines them all and pin it up so everyone can check if they don't understand one. Beats the browsing through pages only to find one little abbreviation.

Now in alphabetical order courtesy of Hekate101!

ADN = Any day now
AFAIC = As far as I'm concerned
AFK= Away from keyboard
AKA = also known as
ASAP = as soon as possible
ASL = age/sex/location
ATM = At the moment
ATM = at the moment
AWOL = Absent Without Official Leave
AYFK = Are you for real?!
AYFS = Are you (censored ) serious?
AYPI = And your point is?
BAS = Boys Are Stupid (no offense to boy members...)
B/C = Because
BBL = be back later
BRB = be right back
BTDT = Been There Done That
BTW = By The Way
CD9 = code 9 (it means parents are around, so don't write that thing about Lucy, for Pete's sake!)
CU = see you
CYA = cover your arse
DD = Dear Daughter
DH = Dear Husband (or darn, depending on you mood, lol==and not to be confused with Deathly Hallows over here )
DL = down-low
DOS = dad over shoulder
DS = Dear Son
DW = Dear Wife
FAQ = frequently asked questions
IFLY = i (censored) love you
FTL = for the lose
FTLOP = for the love of pete!
FTW = for the win
FYI = For Your Information
GAS = Girls Are Saints Stupid (just to show we can take it :P)
GMTA = great minds think alike
GOP = geez o pete
GTG/G2G = either term means got to go
ICCL = I could care less
IDK = I don't know
IFYWIM = If you know what I mean
IHTFP = 'I have truly found paradise' (used sarcastically) or alternatively, 'I hate this (censored) place' lol.
ILY = I Love you
IM(H)O = In My (Humble) Opinion
IYF = In your face
JK = just kidding
JSYK = Just so you know
LMAO = laugh my butt wink.gif off
LMAO = Laughing My Arse Off
L'OMG = LOL, OMG!
LOOMM = Laughing out of my mind
LYKZOMFGSQUEEEE (Exclamation of excitement/surprise, pretty much independent to the site www.says-skills.com )
LYT = Love you too
MOS = mum over shoulder
NMU = not much, you?
noob = newbie. Used as an insult.
OMG = Oh My God
POS = parents over shoulder
RL = real life
ROFL = rolling on the floor laughing
ROFLMAO = rolling on (the) floor laughing my (censored) butt off
ROTFL = Rolling On The Floor Laughing
SOHF = sense of humour FAIL. (love this one)
STFU = Shut the (censored ) up (usually used as a expression)
STP = sooner than possible (made that one up, but it's good, ain't it?)
TBH = to be honest
teh = the
TMI = too much information
TMTH =Too much to handle
TTFN = Ta ta for now
TTYL = Talk to ya later
TYCLOS = Turn your caps lock off, stupid.
w/e = whatever
WB = either 'welcome back' or 'write back'
WTF = what the (censored)
ZOMG = um... OMG with the Z for emphasis


This shall be updated when more are found in the thread below *points* :D