Common Acronyms /Abbreviations 

E-mail acronyms :

R.S.V.P. – This acronym means "Répondez s'il vous plait," French for "respond, if you please." It is often used on invitations to parties and special events, and is intended (as it says) to be responded to with a "yes, we will attend," or "no, we will not."

P.S. – Means "post script." At the end of a letter, people will often include a P.S. to include an extra thought that was intended to be included in the letter, but forgotten. Using a P.S. was more common in typewritten letters, when you couldn’t go back and add a sentence in the body of a letter.

A.S.A.P. – "As soon as possible," used when encouraging someone to respond to a request without delay.

E.T.A. – This acronym means "estimated time of arrival," and is used as a guess for when one expects to arrive while traveling.

B.Y.O.B. – "Bring your own bottle" is used for parties where guests are expected to bring their own beverages.

D.I.Y. – This acronym stands for "do it yourself," which means creating something on your own.  It is often used for crafts and home repairs.

Chat:

ACE  - a cool experience

AD - awesome dude

AFAIK - as far as I know

AFK - away from keyboard

ANI - age not important

BRB - be right back

CUL - see you later

CWYL - chat with you later

IIRC - if I recall/remember correctly

IQ - ignorance quotient

LOL - laugh-out-loud

NP - no problem

ROFL - rolling on the floor laughing

TY - thank you

WC - wrong conversation

Oxford Abbreviation  List 
http://public.oed.com/how-to-use-the-oed/abbreviations/