Compiled from many sources…

AFAIK = As Far As I Know
BTW = By The Way
CMIIW = Correct Me If I’m Wrong

OIC = Oh, I See
OMG = Oh, My God
OTOH = On The Other Hand
CP = Cross-Posting
OT = Off Topic
OOT = Out Of Topic
VOOT = Very Out Of Topic
POV = Point Of View
PS = Post Scriptum; PostScript
SOL = Sorry, One Liner – kalau pesan anda pendek, cantumkan ini.
FYI = For Your Information
HTH = Hope That Helped/Hope This Helps
IAC = In Any Case
IIRC = If I Recall Correctly
IMO = In My Opinion
IMHO = In My Humble Opinion (rarely: In My Honest Opinion)
IMNSHO = In My Not-So-Humble Opinion
IOW = In Other Words
ISO = In Search Of
LOL = Laughs Out Loud
LMAO = Laughing My Ass Off
ROTFL = Rolling On The Floor Laughing
ROTFLMAO = Rolling On The Floor Laughing My Ass Off
SSIA = Subject Says It All
TBE = To Be Expected
TBH = To Be Honest
TWIMC = To Whom It May Concern
TBYB = Try Before You Buy
TMA = Take My Advice
TIMTOWTDI = There Is More Than One Way To Do It
TINALO = This Is Not A Legal Opinion
TINAR = This Is Not A Recommendation
TIA = Thanks In Advance
TFTT = Thanks For The Thought
TYVM = Thank You Very Much
WOMBAT = Waste Of Money, Brains, And Time
WBS = Write Back Soon
WRT = With Regard To; With Respect To
WYGIWYPF = What You Get Is What You Pay For
WYSIWYG = What You See Is What You Get

* less common, usually done by agreement of forum members – CMIIW *

WTB = Want To Buy
WTS = Want To Sell
WTI = Want To Inform
WTA = Want To Ask