I just put a Bushnell Trophy MP on my Sig 522 and my son's M&P 15-22. I'm really impressed with the quality and at $135 shipped from Amazon - it didn't break the bank. Amazon calls it the "tactical elite" other sites call it the Trophy MP - same part #...
http://www.amazon.com/Bushnell-Tact...S8CE/ref=sr_1_2?ie=UTF8&qid=1295707513&sr=8-2
http://www.amazon.com/Bushnell-Tact...S8CE/ref=sr_1_2?ie=UTF8&qid=1295707513&sr=8-2