As everyone has already stated, most of the manufacturers are putting out a very good product. Here's a few companies I'd recommend (In no particular order. If you want exact preferences, PM me.)
Armalite
Bushmaster
Colt
CMMG
DPMS
Rock River
Sabre Defence
Stag Arms
Although I did recommend them, I would pass on the Colt, unless you found a really good deal. Colts tend to bring premium prices because of the Colt name. In my experience, several other companies make a product as good, if not better, than Colt at a lower price. There is nothing wrong with Colts, they make a fine product. They are just a bit more expensive.
Erik