The Aimpoint products are very good, and your choice depends on your applicaton. I agree the mini aimpoint is a great choice.
A less expensive option is a Truglo sight. These are available as 1x power (no magnification) and 2x power. That is item #3 on this website:
Amazon.com: truglo: Sports & Outdoors
I have one of those (#3) on my shotgun, and I like it. It is very sturdy and has been reliable for me.