Trijicon dual illuminated rmr - Trijicon RMR Dual Illuminated 9.0 MOA Green Dot Reflex Sight

This is the best dot available, hands down. Yes, it is expensive, but when you buy from Trijicon, you can trust that you're getting the best. It doesn't need batteries, which means that you never have to bother with it, unlike other dots where you have to remove it from it's base and loose your zero. And the fiber optics are top quality, the dot is as bright as any battery powered dot. I have one both my Sig P220 and my AR10 and neither one has had any problem with 45ACP or 308 rounds or holding a zero after thousands of rounds.