Lot of cheap sights suggested here. However, if you can afford to buy top-of-the-line,... you should seriously check out the Spot-Hogg series. I've used/test and impressive number of sights and nothing has compared to the Hunter Hogg-It model I currently shoot. Once you actually get one in your hands you'll understand the rave reviews and why they are widely regarded as THE standard of excellence.
Good luck and good shootin'
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