I have a Bushmaster and like it. One caveat - when I got it, the barrel wasn't indexed properly; it took about 17 clicks of windage to get on target. A call to Bushmaster and they arranged to have UPS pick up the upper, they fixed it properly, and returned it, all within 2 weeks, at no cost to me. So they DO stand behind their product. (Reliablility was never an issue - the rifle just works.)
Colt's rifles also DO seem to work, but Heaven help you if you need warranty work done. (I had a 1911 Jammamatic that Colt's simply would NOT fix, so IMHO their warranties are meaningless . . . I won't have another Colt in my safe - period.) Also, many of the "civilian" ARs that Colt sells have a block in the lower receiver and non-milspec pins . . . and even after the AWB expired, they won't officially sell rifles with "evil" features like a flash hider to civilians; if you want those on a new Colt, you have to buy - and probably pay a premium for - an LEO market rifle. (Legal most places, but considered "gray market" since Colt's would prefer they only be sold through law enforcement channels.)
Armalite and Rock River AR's also seem to be pretty decent, and I've heard good things about Stag Arms and S&W's series of AR clones.
DPMS quality seems to be spotty - mostly OK, but I've met a more people who've had problems with this brand than the others mentioned.
The only REAL problem rifles on the AR platform seem to be some of the frankenrifles some people have put together out of gun show parts in order to save some money; if you build your own, use good parts. (Duh!)
Oh . . . and be sure to use quality magazines - USGI, Brownell's, etc. Beware of "refinished" or "used" magazines.