To add some more...
u = you
r = are
m = am
i c = I see
b4 = before
w8 = wait
fu = **** you
k = ok = okay = a british way to say that you agree
pro = professional
bs = backstab OR bull****
admin = administrator
gay = commonly used as curse even tho the real meaning is 'male homosexual'
roflolmfao (

) = rolling on the floor laughing out loud my ****ing a** off
wtf = what the ****? (also the only single statement using **** NOT as a curse or flame)
flame/flaming = hurting someone else mentally
SC = Starcraft
WC = Warcraft
D2 = Diablo II
Lotr = Lord of the Rings
RPG = role playing game
mod = moderator(person) / moderation(program)
1337 = leet - langauge based on English that replaces letters with similar ASCII, also considered 'cool' and thus used to determine the word cool.
ya = you/your
yah = yes
wth? = what the hell? - a lighter version of wtf
omg = oh my god!
omfg = oh my ****ing god!
lo' = hello
yo = hiya = hello
GM = game master
rj = rejoin (leave game and enter again in order to refresh your dl)
dl = download
hf = have fun
gj = good job
rm = remake
ums = use map settings
ctf = capture the flag
pr0n = porn
j00 = you
gtg = got to go (like g2g)
exp = expert OR experience
pwn = own
nl = noob lock
nler = noob locker
refresh slots = asking the game creator on bnet to close and reopen empty slots in order to move the game back on top of the games list and draw people into the game.
re = remake OR save replay
rm = remake (play the same game again - usually said as for asking the current players to stay for a next round)
hell = also used as damn/darn
haxer = hacker
SEN = StarEdit Network
SMT = StarEdit Map Team
WB = Warboards
SCC = StarChitChets (WB map&mod team)
PR = Project Revolution (bunch of guys remaking SC into 3D on the WC3 engien)
(U) = Clan UnKnOwN (famous StarCraft mapping clan)
NG = newgrounds
spam = flood with pointless information
flood = type over the same thing a lot
[word]az = [word]er (example: Snipaz actually means Snipers)
bash = flame a lot
Guten Morgen = Good Morning in German -.- (not a net term but I
really wanted to add it...

)
ppl = people
crap = pointless
wa? = what?
WH = WarHammer
sc.org = www.starcraft.org
blizz = Blizzard (the company)
EA = Electronic Arts (the company)
MS = MicroSoft (the company duh...)
lol = laughing out loud OR lots of laugh
comon = come on
zzz = *sleeping*
*[word]* = doing an action (example: "k whatever..." *sniff*)
nvm = never mind
pix = pictures
hax = hacking OR hacks