I like the Weaver Tactical 3-10 mil/mil scope from Midwayusa they are on sale right now for $300. I like to better than the previously mentioned Buckmaster 6-18.
The one awesome thing about this scope is that the reticle matches the turrets, basically if you miss the target or your intended point of aim if you spot it in the scope use the reticle to measure how many mils you were off by and plug that number into the turret on the scope.
Ex: shooting at a target, you miss your point of aim, you were roughly 1.5 mil low and .5 left, plug those into your scope turrets and you should hit dead center or darn close.