I have to agree with Beowolf the EO Tech sight is first rate. They just released a new version that is for military use, it's much more rugged and reliable. This site allows very quick aquisition of a target from the low ready position. It works well for distances up to 200 yards,and you are afforded an excellent field of view. But once again the ACOG is the heat for anything farther than that, which you will see in A-stan.
I would suggest two sights at a minimum, you cant use one tool for every job. Also the old ACOG suggestion is correct. Save some money. and spend it on good magazines, but thats another discussion.