ACK! An exclamation, as in "Ack, I dropped my toothbrush!" or "ACK! My cat's on fire!"
ACME The supplier of all bizarre, unique, and usually dysfunctional items.
AFAICT As Far As Can Tell
AFAICTM As Far As I Can Throw Manhattan (this being a measure of trust)
AFAIK As Far As I Know
AFK Away From Keyboard
Alpha Geek The most knowledgeable, technically oriented person in the area. "Ask Confi, he's our resident Alpha Geek." (see also: house wizard)
AOL Almost on Line
BAD Broken As Designed (I think that says enough about something)
Barf to complain about "What are you barfing about?"
or to throw up
BBIAB Be Back In A Bit
BBL Be Back Later
BBS Be Back Soon
Beige Toaster how one usually refers to a Mac Classic (the one-piece) ™-G
BF boyfriend
brain fart (see below)
Big Red Button The one that turns off everything. Usually labeled "Do NOT Press Big Red Button!!!" Sometimes seen as the BRS - Big Red Switch
Biznatch An insult. Drop the -zna- ™-Evek
Black hole Where all lost e-mail disappeared to
Blowing one's buffer To lose one's train of thought. When the person you are speaking too says something so astonishing that you loose your train of thought: "Whoa, you just blew my buffer!"
BOAJ Butt Of All Jokes - if you don't know who this is, it's probably you.
Brain fart a stupid error, when one knew better, e.g. typing in 'dir' in Unix, after playing with DOS
BRB Be Right Back
BTW By The Way
Bzzzzt, wrong! If you don't know, watch Family Feud, sometimes seen in its longer form "Bzzzt, wrong. Thanks for playing!"
Dead cow What hamburgers are made from
Dead Tree Edition a hard-copy, the paper edition of an electronic text, i.e. a book
.dic Short name for this file (not to be confused with a .dick, which is pretty obvious)
DOA Dead On Arrival (often used to describe bad software)
D'oh! Thank you, Homer Simpson
DMS Drunken Mouse Syndrome, when your pointer jumps around erratically, and doesn't go where the mouse goes. Can be fixed by cleaning your mouse ball.(Yes, mice only have one ball.)
Evil Something too complicated to deal with,... with the implication that the programmer was just stupid, as opposed to being "rude" (see below), though, the two may be used together to describe something completely bad, as "evil and rude"
FAQ Frequently Asked Questions
FDL Falls Down Laughing
FUBAR Fucked Up Beyond All Recognition (sometimes 'Repair,' but in all truthfulness, if something gets to the point of being FUBAR, the two words are pretty much interchangeable)
FYI For Your Information
GF Girl-Friend
Gray Bar Land Completely zoned out, from watching the little gray bar (now blue in recent versions of IE) at the bottom of the web browser window slowly move as a page loads.
House Wizard A very technically skilled individual (see also: Alpha Geek)
Huggle Something of a cross between "hug" and "cuddle," whoever thought of this should be shot
IAW In Another Window
IBM I Blame Microsoft
Inferior, But Marketable
I'd Buy (a) Mac
IMHO In My Humble Opinion
IMNSHO In My Not So Humble Opinion
IMO In My Opinion (you get the idea)
IRL In Real Life (as opposed to on the internet)
JK (or j/k) Just kidding
Kewl Cool, written phonetically (sort of)
Keyboard Plaque The grime that build up on a keyboard, making keys sticky and sometimes causing them to change color. Usually made up from a combination of coffee, soda, Doritos, and other snack foods
Laff Laugh
LOL Laughs Out Loud
Macintosh Most Applications Crash, If Not Then Operating System Hangs
MIA Missing In Action. Someone who never answers e-mail anymore, or has gone 404 (see below), though there is the implication that the individual was once normal (or close to) at some point in the past.
No Brainer simple task, that even a person without a brain could do
PEBKAC An error type, stands for "Problem Exists Between Keyboard And Chair"
PITA Pain In The Ass
Pop a squat Have a seat ™-Jynx
PPL People
PPLZ The plural of ppl (why? Who knows? …or cares?)
Random Something out of the ordinary, unexpected, for example: "Whoa, that flying pink elephant was random."
Re (re-hi) Hello again
ROTFL(MAO)(ASTC) Rolls On The Floor Laughing (My Ass Off) (And Scaring The Cat)
RTFM Read The Fucking Manual!!!
Rude Something too complicated to understand, with the implication of malice in the item's origin (see: evil)
Smile and nod What you do when you don't understand, care, or have any real desire to do either ™-G
SNAFU Situation Normal, All Fucked Up
Snail mail Physical mail, through the U.S. Postal Service (called 'Snail' due to its speed, compared to e-mail)
Snarf To accidentally spew water (or other liquid, or even food if it's bad enough) usually through the nose due to a fit of laughter. "Your e-mail was so funny, I snarfed my soda."
Three Finger Salute Control-Alt-Delete (aka: Vulcan Nerve Pinch)
Thwap To hit, or a hit, usually includes the usage of a random (see: random) device. "Ack, I've been thwapped with a bag of potatoes!"
TTFN Ta-Ta For Now
TTY(time) Talk To You (insert letter here: 'L' for later, 'S' for soon, you get the idea)
Vulcan Nerve Pinch Control-Alt-Delete (aka: three finger salute)
WTF? What The Fuck?!?! An exclamation of surprise and confusion
WWIT? What Wierdness is This? ™-Jynx
WYSIALG What You See Is ALL You Get - similar to WYSIWYG, but infers that the item at hand is a little under par...
WYSIWYG What You See Is What You Get
308 Cannot connect to site, Site may be down. For that particular individual who you just cannot get through to. "Don't bother trying to get through to him, he's 308." Sometimes because the person is 404 (see below)
403 Access denied, when you don't get something you want, or think you should have. "Damn it, I got 403'd" i.e. nothing. Also used by some individuals as "No Comment."
404 A person who is clueless, or lost. Comes from the web response "404, file not found"

If you didn't find it here, check the Wikipedia, it has everything.