Out of all the scopes I've used on different AR's the two that I thought were the most useful were the Leupold MK4 MR/T 2.8-8X36 and a Weaver Grand Slam Tactical 3-10X40 (MidwayUSA exclusive.)
Both are about the "right size" for the AR platform and work really well for the type shooting you discribe. Both have exposed turrets and do have the "tacticool" look to them. The Weaver is a real bargin at $299. The glass is about equal to the Leupold. The Leupold is one of the most forgiving scopes I've ever used as far as eye placement goes and probably a better choice if fast shots are important.
