Pistol calibers:
9mm luger
7.62x25mm
10mm
40 S&W
45 ACP
.50 AE

Rifle calibers:
.17 HM2
.17 Remington
.22 Long Rifle
.204 Ruger
5.45x39mm
222 Remington Magnum
.223 Remington
.223 WSSM
.223 Wylde
5.56x45mm NATO
.243 Winchester
.260 Remington
5.7 x 28
6mm PPC
6mm AR
6mm-223 Remington
6.5 Grendel (.264 cal)
6.8 SPC (.270 cal)
.300 Whisper
.300 Remington SAUM
7.62x39mm
.338 Federal
.450 Bushmaster
.458 SOCOM
.50 Beowulf
.50 BMG
.500 Phantom

Found this on the web thought it was helpful and I would share it.  Here is the web link to give credit http://en.wikipedia.org/wiki/AR-15

Added a few already.  Help me keep them in size order please, I need help with that. So which calibers are the most common?  I will underline them.

Let's not forget many more, almost anything that fits.  .17 HM2 is the smallest followed by the .17 Remington, then step up to the 5.7 x 28 and we can then fill in almost everything from the entire line of WSSM cartridges followed by countless wildcats, such as the .500 Phantom (while full advantage is gotten in the AR-10/LR-308 platform it can work in the AR-15 platform as well).  
I'm afraid the list is not almost complete, and likely never will be.  Thank goodness!

357Sig, 440Corbon & 40Xtreme. I know theres more.

Thanks I am trying to stay with the ar15.  I am just trying to build a list.  So are the 499 LW, 45 Professional, 6mmWoa, 300/221 fireball, 470 Rhino--AR 15 or AR 10?

Quoted: That list is woefully incomplete/incorrect... not being a jerk just being honest. Off the top, 499 LW, 45 Professional, 6mmWOA, 300/221 fireball, 6,5 creedmore (AR10), the 470 Rhino, and its offshoots. Furthermore, the 308 does NOT fit into the AR 15, it is in the AR 10 platform, unsure if you just were being general to the design or specific to the platform but lets be clear there is a difference. Ahh wikipedia.... I rarely use wikipedia and only consider doing so when I know nothing and need a quick and dirty 9th grade run down of the topic...thats what the circles I work in think of it anyways...

Quoted: Ahh wikipedia.... I rarely use wikipedia and only consider doing so when I know nothing and need a quick and dirty 9th grade run down of the topic...thats what the circles I work in think of it anyways....

It's a general encyclopedia, so it's generally sufficient for general topics.

The specialist topics are hit-or-miss.

I wouldn't crack open a [print] general encyclopedia (e.g. Encyclopedia Brittannica, Encyclopedia Americana) expecting to find informative, expertly-written specialist topics (i.e. technically accurate AR-platform stuff, soils science, hydrology).

I would go to a specialist encyclopedia (e.g. Encyclopedia of Plant and Soil Science, Encyclopedia of Materials Science, Encyclopedia of Nanotechnology).

One cool thing about Wikipedia, though.... sometimes the people writing the entry for the [for example] high-energy physics stuff are the same ones simultaneously publishing their latest work in peer-reviewed academic journals.

But still hit-or-miss.

Quoted: Quoted: Ahh wikipedia.... I rarely use wikipedia and only consider doing so when I know nothing and need a quick and dirty 9th grade run down of the topic...thats what the circles I work in think of it anyways.... It's a general encyclopedia, so it's generally sufficient for general topics. The specialist topics are hit-or-miss. I wouldn't crack open a [print] general encyclopedia (e.g. Encyclopedia Brittannica, Encyclopedia Americana) expecting to find informative, expertly-written specialist topics (i.e. technically accurate AR-platform stuff, soils science, hydrology). I would go to a specialist encyclopedia (e.g. Encyclopedia of Plant and Soil Science, Encyclopedia of Materials Science, Encyclopedia of Nanotechnology). One cool thing about Wikipedia, though.... sometimes the people writing the entry for the [for example] high-energy physics stuff are the same ones simultaneously publishing their latest work in peer-reviewed academic journals. But still hit-or-miss.

I have taken college class and they say not to use wikipedia as a source, but I'm not writing a college paper here. I don't put my full trust in the information that comes out of this site most of the time. I use it as a guide because forums are made of opinions  I'm just trying to put together a list and wikipedia did help me get it started.  So lets fix it and get it right, instead of talking about wikipedia.  So please help me.

From the archives

http://archive.ar15.com/forums/topic.html?b=3&f=121&t=311683

.17 Remington
.204 Ruger
.221 Fireball
.22 PPC
.222 Remington
.223 Remington
.223 WSSM
6mm PPC
.243 WSSM
.257 WSSM
6.5 Grendel
6.8 SPC
.300 Whisper
.30 Carbine
7.62x39
.338 Spectre
.450 Bushmaster
.458 SOCOM
.499 LW
.50 AE
.50 Beowulf

.22 LR
9x19
40 S&W
10mm Auto
45 ACP
9x23 Win
7.62x25 Tokarev


Wildcats or rounds for which factory ammo is not available:

Numerous .17's
.20 Vartag
.20 Vartag Turbo
.20 Tactical
5.45x39
.22 Lindahl Chucker
.240 Madame
6mm-222
6x45
6mm TCU
6mm WOA
6mm AR
.25/222 Copperhead
.257 TCU
.265 1*
7mm Whisper
.30 HRT
.30 PPC
.30 PPC LONG
8mm HRT
.357 Auto
.38 Casull
.40 Super
.40 Extreme
.440 Cor-Bon
.475 Tremor
.500 Phantom
.502 Thunder Sabre

BUt even that list is not complete..

I think the list should include a list of mfgs for some of these odd balls.

Bohica Arms makes bolt action uppers in...

50 DTC-EDM Spec
416 Barrett
338 Lapua Magnum

I have given up on the list because everyone say the list is a never ending one.  I didn't know there was so many calibers.  I was just looking for the main one but I know what they are.  So thanks for the help guys.

The list really is never ending, considering I have some barrels here chambered in calibers I have developed but not shared ... and I am sure there are others out there who have done the same.  As long as there are people wildcatting rounds, there will be new and additional calibers chambered in the AR platform.

Marty, you had a pretty good list posted on the 458 socom forum