Generally, any of the high end large objective scopes will do really well. I tend to use the Tangent 3-15x50 TT315M, like the gentleman above, but if you can spend the cash on S&B Polar 4-16x56, it will be probably do a hair better.
That having been said, before you spend that much money, I would try Meopta Meostar R1 3-12x56 or R2 2.5-15x56. The first one is definitely within your current budget and you'd be surprised how well they do in low light.
ILya
