Well, as a start you can check out the monthly round-up from right here at Tom's Hardware. Here's a link to the mid range section of cards for this month:
http://www.tomshardware.com/reviews/best-graphics-card,2964-3.html
That' being said, we'd need to know things like:
Whether your Mobo/case can fit a dual-slot cooler card
Whether you are looking to spend over $200/$300/etc...
What the rest of your rig stacks up like so we didn't recommend a card that is beyond the rest of your rig (causing a performance bottleneck, and a waste of money)
Hope that helps a little.