Pricey but worth it - EOTech HOLOgraphic Sight 557 w/ G23 3x FTS Magnifier Weapon Sight System w/ FREE ScopeCoat Protective Covers and AA batteries

Facilitates quick transition from close quarters battle to long range with one holo sight. Allows reliable, accurate shooting with both eyes open, lightening fast target acquisition, and easy range estimating. The BDC reticle is accurately tuned to 5.56 caliber out to ~ 600M. Sets up in seconds on the rail and re-sets to zero when removed/replace. Battery lasts for close to a thousand hours (with lithium; a bit shorter with alkaline). Side mounted controls don't interfere with the magnifier or backup sights. Halo is easy to see in any light conditions and is nightvision compatible. Magnifier works much better than cheap knockoffs, particularly in low light. Fantastic package; highly recommended!
Pros: Robust, accurate, waterproof, BDC reticle, tuned to 5.56, night vision compatable
Cons: Expensive

This review was written in the old system and had content requirements that are different than reviews written today.