Sorry, goms, had a busy weekend.
The original "AR" was actually the AR-10 in 7.62 (.308). The AR-15 (5.56) came later. The .308 AR platform will shoot a whole family of calibers based on the .308 case. It includes besides the .308Win, the 260Rem (6.5mm), the 7mm-08 and the .338Fed (~8mm). (There may even be a 6mm and a 5.5mm caliber, too.) All use the same case, just necked up or down to the caliber. That means only the barrel (upper) needs to be changed. The lower and the magazines all work with all the calibers.
There are numerous manufacturers of this style. Here are a few links.
http://www.dpmsinc.com/firearms/firearm.aspx?id=14http://www.bushmaster.com/index.asphttp://www.lesbaer.com/UltMonolith-MID-SWAT.htmlIn other "tactical" designs of semi-autos that shoot the .308, (besides the FN FNAR) there's the venerable FN FAL. Most widely adopted auto rifle. I think the list of countries runs around 90 that have adopted it at one time or another. There are many variations, many manufacturers (mostly overseas). Here's the Wikipedia link about it.
http://en.wikipedia.org/wiki/FN_FALAnd a current US manufacturer.
http://www.dsarms.com/FAL-SA58%20Rifles/products/8/Last, but certainly not least is the US M1A1, the semi-auto of the M14. It comes in varying models, like SOCOM, scout/tanker, sniper and match version. I only separate it out from the others because it is unique from the AR and FN platforms. The M1A is available in traditional wood stock and in tacti-cool configurations. Here's a couple of links
http://www.springfield-armory.com/armory.php?model=13http://www.selwayarmory.com/sfsocomm1arifle308bluedblackcompositestock.aspxhttp://www.fulton-armory.com/M14-Rifles.aspxThere are many more manufactures but I hope that gets you started. Alf
If any of the links don't work, just go to the basic domain (xxxxxxxx.com) and drill down for the appropriate product.