Any nice target scope will work. Check out
www.riflescopes.com and make sure to click on the "Sample List" link as there are some good deals. If you want to keep it "Tacticool" you can put an ACOG on there which will give you 3.5-4x. If you really want to spend some dough look into a Nightforce scope. Like elderboy I just have a EoTech 551 on mine.