As far as smaller, single red dotsights go, I've been happy with these two.

http://www.opticsplanet.net/burris-fastfire-w-picatinny-mount-4-moa-dot-mat-fastfire-sight.html#

http://www.opticsplanet.net/atn-corp-cmp-dusrs.html

And as has been said, the Stryker sight is nice but much larger.

As you'll see, the Optics Planet site has many to choose from.

Mike