I'm a fan of 2-7 Scopes on my AR's. My two favorites are the vortex viper 2-7x32 with the C3 recticle and the redfield 2-7x32 with the accu-range recticle. Both are easy to shoot up close on 2x and then they can be dialed up to shoot for precision out to 300 yards.
As far as scope mounts go I have had good luck with the Burris pepr and the RRA cantilever. The RRA mount is a few dollars less than the Burris but just as ruggedly constructed.