if you go open sights, fiber optic(or tritium maybe?) would be best. TruGlo offers several options, but they are the only name I can think of off the top of my head.

I would have to agree with stalkingbear and say go with a low power scope. I used a fixed 2x scope on my M4 when I was in the service, and target aquisition time was VERY quick, but thanks to the 2x magnification, had a perfect sight picture. I would suggest that if you went with a scope, using a forward mount with it, similar to Ruger's Forntier Rifle. This allows you for quick targeting with both eyes open, then shutyour non-shooting eye and you have magnified sight picture. Takes a bit of practice, but well worth the investment.