Colt SP6920 or a BCM if you want a middy. There is also the option of Spike's for a good middy. If you want a precision gun, LaRue, Noveske and BCM all sell precision AR's for a decent sum, but the accuracy you get pays you back.
S&W's may be okay, though I don't believe they're full mil-spec. RRA's might also be okay but I've heard bad stuff about their assembly process (torquing, materials, etc.).
Doublestar and Del-ton are not what I'd call decent, stay away from Bushmaster and DPMS.