Click this link (Snipers Hide custom Google search engine), type you question in the box and you will get a multitude of threads for a subject that has been covered ad nauseum.
Most of them are "decent" and reliable enough for what you will most likely use it for. Kind of depends on your price range and your interest in details after that.
Build your own...Seriously! There's nothing to it. Start with a barreled upper from Bravo Company and a self-assembled lower of your choice. I built my first one in under an hour with no problems.
I couldn't be more pleased with my Rock River Preditor Pursuit. It shoots well under the 3/4" promise and the trigger is excellent right out of the box not requiring a change which is more than I can say about Colts and Bushmasters I've owned. Regards
I would suggest getting ahold of specialized dynamics. The owner is great to do bussiness with and will make the AR specific to your needs. His name is Scott and his prices are very nice!
It helps to provide a little more information about what your plans are for the rifle...
Is it for home defense, tactical or carbine classes, competition, hunting, duty weapon or just a range gun?
Take a look at this read thru page 10 or less you'll find alot of information that may guide you in the right direction. It did for me... http://forums.officer.com/showthread.php?81462-So-you-want-to-buy-an-AR-15-huh
Good luck on your build or buying!