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