People are going to suggest Asus DC2 based GTX 670s because of their superior cooling, but not at the prices they're being sold at ($420+). They are not worth that extra $30+ for the small bit of extra oc you can do.
I'd ignore the GTX 680 and 7970 (non ghz edition) because they're pretty much for people who want that extra 5% performance and got extra $100 to blow.
And get a 7970 GHZ edition if you can afford it. that's probably the most sensible high end GPU right now.