Nikon Bolt XR, the one that came with my bow was crap, I read up on a lot of scopes and there are several good one out there from reviews but Nikon scopes have never done me wrong so I went with them. I don't care for a illuminated reticles(most x-bow scopes have this) and the Nikon DOESN'T but are great in low light so that was one thing. The scope is small, light weight, and solid built. Nikon also has a online distance calculator for your scope distances that is fairly accurate. It was very easy to sight in also.
Cost me $140.00 to my door and I heard of other getting it for 100 even but I couldn't find that deal at the time I wanted/decided to buy it.