Here is a start:

lol = laugh out loud/laughing out loud
lmao = laugh my @$$ off
roflmao = rolling on the floor laughing my @$$ off
lool = laughing out outrageously loud
fdlmao = falls down laughing my @$$ off
fdl = falls down laughing
brb = be right back
bbl = be back later
b2b = business to business
ttyl = talk to you later
ttfn = ta ta for now
tfn = til further notice
bol = busts out laughing
lmfao = laughing my fat @$$ off
lmbo = laughing my butt off
imho = in my humble opinion
imo = in my opinion
rtfm = read the f* manual
<3 = love (heart)
h8 = hate
tmi = too much info
omg = oh my gosh
omfg = oh my f* gosh
itt = in this thread
afaik = as far as I know
afk = away from keyboard
asl = age sex location