Here are some to be going on with - please feel free to add others that you know or want to know.

ACRONYM MEANING

AFAIK As Far As I Know
AKA Also Known As
ASAP As Soon As Possible
ATM At The Moment
BTW By The Way
DD Dear/Darling Daughter
DH Dear Husband
DP Dear Partner
DS Dear Son
FAQ Frequently Asked Questions
FWIW For What It's Worth
FFS For F**x sake
FYI For Your Information
HTH Hope This Helps
IMO In My Opinion
IMHO In My Humble Opinion
IMNSHO In My Not So Humble Opinion
IYKWIM If you know what I mean
IYSWIM If you see what I mean
LMAO Laughing My Ass Off
LOL Laugh/ing Out Loud
OMG O My God!
PITA Pain In The Ass
POV Point Of View
RL Real Life
ROFL Roll/ing On the Floor Laughing
RAOFLMAO Rolling Around On the Floor Laughing My Ass Off!
TY Thank you
YW Youre welcome
WB Welcome Back
WTG Way To Go
WTHDTM What The Hell Does That Mean
WYSIWYG What You See Is What You Get
WTF What the f*ck

BM Birth Mother
ED/S Elder Daughter/Son
SD Step Dad
SD Step Daughter
SM Step Mother/mum
SO Significant Other
SS Step Son
YD/S Young(er) daughter/son

MIL and FIL etc
Mother in law, Father in law..also SIL and BIL Sister and Brother in law

OH - Other Half

TMI - Too Much Information

OT Off topic

OP - Original poster (IE the person who starts a thread)

SP(?) - Spelling (used if you're not sure how something's spelled)

SO - Significant Other