Rock Rivers are hard to beat for out of the box reliability & accuracy. But I wouldn't have a problem buying a Colt, Stag Arms, DPMS, or Bushmaster. My favorite is my Les Baer, but then at $2K, there are a lot of other really nice AR's such as Noveski, Laru Tactical, Daniel Defense, and several other high end models.
One of my cheapest AR-15's that I really like is my S&W M&P. Great gun for the money.
I also noticed the other day that CDNN Sprorts has their MagPul Colt AR-15's on sale for $949. Which sounds like a really good price to me.
http://www.cdnnsports.com/6920mp-223-le-moe-bl-fde-16-fl.html#.U8XGqPF5mSM