Go for the typical black rifle optics....
Aimpoint, Eotech, ACOG, S&B Short Dot or cheaper Bushnell red dots etc as budget dictates. Personally, I like Aimpoints but havent had much experience with the S&B products and those users tend to rave about them...
The cheaper optics arent bad for the money but, well, there is a difference between a $60 optic and a $1000 optic and the difference often becomes very apparent very quickly...