I picked up one of these at the NRA Annual Meeting, heavily discounted. I had planned to use it for my next build. But I love carrying it around when I go for walks, that I might not mount it. 700 lumens is nuts.
http://sigsauer.com/SigStore/ShowProductDetails.aspx?categoryid=26&productid=263
On my Bushmaster I'm running a Millett Zoom Dot. Had some issues with the battery. So I found their cust. service guy at the NRA show here and he totally hooked me up, took the thing apart, showed me everything, gave me a new battery. Very cool cust. service.
http://www.millettsights.com/controller.php/cat09/zoom_dot