Way too many to list them all I am sure, and I don't know (idk) many. But:
hru - how are you
lol - laughing/laughs out loud
wb - welcome back
brb - be right back
Hope that's a start for you
Also
! I have a comment
? I have a question
@TEOTD At The End Of The Day
^5 High Five
^RUP^ Read Up Please
^URS Up Yours
<3 Heart
02 Your (or my) two cents worth
1174 Nude club
121 One to one
1337 Elite
143 I love you
14AA41 One for All and All for One
182 I hate you
19 0 hand
20 Location
2B or not 2B To Be Or Not To Be
2BZ4UQT Too Busy For You Cutey
2G2B4G Too Good To Be Forgotten
2G2BT Too Good To Be True
2moro Tomorrow
2nite Tonight
2U2 To You Too
404 I haven't a clue
411 Information
420 Marijuana
459 I love you
4COL For Crying Out Loud
4EAE ForEver And Ever
4ever Forever
4NR Foreigner
4Q F*** You
5FS 5 Finger Salute
8 Oral sex
86 Out of, over, to get rid of, or kicked out
9 Parent is watching
99 Parent is no longer watching
A/S/L/P Age/Sex/Location/Picture
A3 Anyplace, Anywhere, Anytime
AAAAA American Association Against Acronym Abuse
AAF As A Friend
AAK Asleep At Keyboard
AAMOF As A Matter Of Fact
AAMOI As A Matter Of Interest
AAR At Any Rate
AAR8 At Any Rate
AAS Alive And Smiling
AATK Always At The Keyboard
AAYF As Always, Your Friend
AB *** Backwards
ABITHIWTITB A Bird In The Hand Is Worth Two In The Bush
ABT2 About To
ACD Alt Control Delete
ACE Access Control Entry
ACK Acknowledgement
ACORN A Completely Obsessive Really Nutty person
ADAD Another Day Another Dollar
ADBB All Done Bye Bye
ADIH Another Day In Hell
ADIP Another Day In Paradise
ADN Advanced Digital Network -or- Any Day Now
ADR Address
AEAP As Early As Possible
AFAGAY A Friend As Good As You
AFAHMASP A Fool And His Money Are Soon Parted
AFAIC As Far As I'm Concerned
AFAICS As Far As I Can See
AFAICT As Far As I Can Tell
AFAIK As Far As I Know
AFAIR As Far As I Remember
AFAIU As Far As I Understand
AFAIUI As Far As I Understand It
AFAP As Far As Possible
AFAYC As Far As You're Concerned
AFC Away From Computer
AFDN Any F***ing Day Now
AFGO Another F***ing Growth Opportunity
AFIAA As Far As I Am Aware
AFINIAFI A Friend In Need Is A Friend Indeed
AFJ April Fools Joke
AFK Away From Keyboard -or- A Free Kill
AFPOE A Fresh Pair Of Eyes
AFT About F***ing Time
AFZ Acronym Free Zone
AGB Almost Good Bridge
AGKWE And God Knows What Else
AIAMU And I'm A Monkey's Uncle
AIGHT All Right
AIH As It Happens
AIMB As I Mentioned Before
AIMP Always In My Prayers
AISB As I Said Before
AISE As I Said Earlier
AISI As I See It
AKA or a.k.a. Also Known As
ALAP As Late As Possible
Alcon All Concerned
ALOL Actually Laughing Out Loud
ALOTBSOL Always Look On The Bright Side Of Life
ALTG Act Locally, Think Globally
AMAP As Many As Possible -or- As Much As Possible
AMBW All My Best Wishes
AMF Adios Mother F***er
AML All My Love
AMRMTYFTS All My Roommates Thank You For The Show
ANFAWFOS And Now For A Word From Our Sponsor
ANFSCD And Now For Something Completely Different
ANGB Almost Nearly Good Bridge
AOAS All Of A Sudden
AOB Abuse Of Bandwidth
AON Apropos Of Nothing
AP Apple Pie
AS Ape Sh** -or- Another Subject
ASAFP As Soon As F***ing Possible
ASAMOF As A Matter Of Fact
ASAP As Soon As Possible
ASAYGT As Soon As You Get This
ASL Age/Sex/Location
ASLMH Age/Sex/Location/Music/Hobbies
ATAB Ain't That A *****
ATC Any Two Cards
ATSL Along The Same Line
ATST At The Same Time
ATW All the Web -or- Around the Web
AWC After While, Crocodile
AWGTHTGTTA Are We Going To Have To Go Through This Again
AWHFY Are We Having Fun Yet?
AWLTP Avoiding Work Like The Plague
AWNIAC All We Need Is Another Chair
AWOL Absent Without Leave
AWTTW A Word To The Wise
AYC Aren't You Clever -or- Aren't You Cheeky
AYCE All You Can Eat
AYK As You Know
AYSOS Are You Stupid Or Something
AYTMTB And You're Telling Me This Because
AYV Are You Vertical?
B&F Back and Forth
B/C Because
B4 Before
B4N Bye For Now
B4U Before You
B4YKI Before You Know It
BAC Bad *** Chick
BAG Busting A Gut -or- Big *** Grin
BAK Back At Keyboard
BAMF Bad *** Mother F***er
banana Penis
BAU Business As Usual
BB Be Back
BB4N Bye Bye for Now
BBAMFIC Big Bad *** Mother F***er In Charge
BBB Bye Bye Babe -or- Boring Beyond Belief
BBBG Bye Bye Be Good
BBFBBM Body By Fisher, Brains By Mattel
BBFN Bye Bye for Now
BBIAB Be Back In A Bit
BBIAF Be Back In A Few
BBIAS Be Back In A Sec
BBIAW Be Back In A While
BBL Be Back Later
BBMFIC Big Bad Mother F***er In Charge
BBN Bye Bye Now
BBR Burnt Beyond Repair
BBS Be Back Soon -or Bulletin Board Service
BBSD Be Back Soon Darling
BBSL Be Back Sooner or Later
BBT Be Back Tomorrow
BBW Big Beautiful Woman
BCBG Bon Chic Bon Genre -or- Belle Cu Belle Geulle
BCBS Big Company, Big School
BCNU Be Seeing You
BCOZ Because
BD Big Deal -or- Baby Dance -or- Brain Drain
BDBI5M Busy Daydreaming Back In 5 Minutes
BDC Big Dumb Company -or- Big Dot Com
BDN Big Damn Number
BEG Big Evil Grin
beos Nudge
BF Boyfriend -or- Best Friend -or- ***** Features
BFD Big F***ing Deal
BFE Bum F*** Egypt
BFF Best Friends Forever
BFFN Best Friends For Now
BFFTTE Best Friends Forever Til The End
BFN Bye For Now
BFR Big F***ing Rock
BHAG Big Hairy Audacious Goal
BHG Big Hearted Guy -or- Big Hearted Girl
BHOF Bald Headed Old Fart
BI5 Back In Five
BIBI Bye Bye
BIBO Beer In, Beer Out
BIF Basis In Fact -or- Before I Forget
BIL Brother-In-Law
BIOIYA Break It Off In Your ***
BIOYE Blow It Out Your Ear
BIOYIOP Blow It Out Your I/O Port
BIOYN Blow it Out Your Nose
***** Basically In The Clear Homey
BITD Back In The Day
BITFOB Bring It The F*** On, *****
BJ ********
BJJDI Billy Joel Just Drove In
BKA Better Known As
BL Belly Laughing
BLBBLB Back Like Bull, Brain Like Bird
BM Byte Me
BMF Bad Mother F***er
BMGWL Busting My Gut With Laughter
BMOF Bite Me Old Fart
BMOTA Byte Me On The ***
BNDN Been Nowhere Done Nothing
BNF Big Name Fan
BO Bug Off -or- Body Odor
BOB Battery Operated Boyfriend
BOBFOC Body Off Baywatch, Face Off Crimewatch
BOCTAAE But Of Course There Are Always Exceptions
BOFH Bastard Operator From Hell
BOHICA Bend Over Here It Comes Again
BOTEC Back Of The Envelope Calculation
BOTOH But On The Other Hand
BPLM Big Person Little Mind
BR Bathroom
BRB Be Right Back
BRT Be Right There
BS Big Smile -or- Bull Sh** -or- Brain Strain
BSAAW Big Smile And A Wink
BSBD&NE Book Smart, Brain Dead & No Experience
BSEG Big Sh** Eating Grin
BSF But Seriously, Folks
BSOD Blue Screen of Death
BT Byte This
BTA But Then Again -or- Before The Attacks
BTDT Been There Done That
BTDTGTS Been There, Done That, Got The T-shirt
BTFO Back The F*** Off -or- Bend The F*** Over
BTHOOM Beats The Heck Out Of Me
BTN Better Than Nothing
BTSOOM Beats The Sh** Out Of Me
BTTT Back To The Top -or- Bump To The Top
BTW By The Way
BTWBO Be There With Bells On
BTWITIAILW/U By The Way I Think I Am In Love With You
BW Best Wishes
BWDIK But What Do I Know
BWL Bursting With Laughter
BWO Black, White or Other
BYKT But you Knew That
BYOA Bring Your Own Advil
BYOB Bring Your Own Bottle -or- Bring Your Own Beer
BYOW Build Your Own Website -or- Bring Your Own Wine
BZ Busy
C&G Chuckly and Grin
C/P Cross Post
C/S Change of Subject
C4N Ciao For Now
CAAC Cool As A Cucumber
CAS Crack A Smile
CB Chat Brat -or- Coffee Break
CBB Can't Be Bothered
CBF Can't Be F***ed
CBJ Covered ********
CD9 Code 9 - it means parents are around
CF Coffee Freak
CFV Call For Vote
CHA Click Here Asshole
CIAO Goodbye (in Italian)
CICO Coffee In, Coffee Out
CICYHW Can I Copy Your Home Work
CID Consider It Done -or- Crying In Disgrace
CIS CompuServe Information Service
CLM Career Limiting Move
CMAP Cover My *** Partner
CMF Count My Fingers
CMIW Correct Me if I'm Wrong
CMU Crack Me Up
CNP Continued in Next Post
COB Close Of Business
COD Change Of Dressing
CofS Church of Scientology
COS Change Of Subject
C-P Sleepy
CRAFT Can't Remember A F***ing Thing
CRAP Cheap Redundant Assorted Products
CRAT Can't Remember A Thing
CRAWS Can't Remember Anything Worth A Sh**
CRB Come Right Back
CRBT Crying Real Big Tears
CRDTCHCK Credit Check
CRS Can't Remember Sh**
CRTLA Can't Remember the Three-Letter Acronym
CS Career Suicide
CSA Cool Sweet Awesome
CSL Can't Stop Laughing
CSN Chuckle, Snicker, Grin
C-T City
CTA Call To Action
CTC Choking The Chicken -or- Care To Chat
CTO Check This Out
CU See You -or- Cracking Up
CUATU See You Around The Universe
CUL8R See You Later
CULA See You Later Alligator
CUNS See You In School
CUOL See You OnLine
CUZ Because
CWOT Complete Waste Of Time
CWYL Chat With You Later
CX Cancelled
CY Calm Yourself
CYA Cover Your *** -or- See Ya
CYL See You Later
CYM Check Your Mail
CYO See You Online
CYT See You Tomorrow
D&M Deep & Meaningful
DAMHIKT Don't Ask Me How I Know That
DARFC Ducking And Running For Cover
DBA Doing Business As
DBABAI Don't Be A ***** About It
DBD Don't Be Dumb
DBEYR Don't Believe Everything You Read
DD Due Diligence
DDD Direct Distance Dial
DDSOS Different Day, Same Old Sh**
def Definitely
DETI Don't Even Think It
DF Dear Friend
DFLA Disenhanced Four-Letter Acronym (that is, a TLA)
DGA Don't Go Anywhere
DGT Don't Go There
DGTG Don't Go There Girlfriend
DGYF Damn Girl You're Fine
DH Dear Husband
DHYB Don't Hold Your Breath
DIAF Die In A Fire
DIC Drunk In Charge
DIKU Do I Know You
DILLIGAD Do I Look Like I Give A Damn
DILLIGAS Do I Look Like I Give A Sh**
DINK Double Incomes, No Kids
DIRFT Do It Right the First Time
DISTO Did I Say That Outloud?
DITR Dancing In The Rain
DITYID Did I Tell You I'm Distressed
DIY Do It Yourself
DKDC Don't Know Don't Care
DL Download -or- Dead Link
DLTBBB Don't Let The Bed Bugs Bite
DLTM Don'