I already bought the GTX680 (though in retrospect, I should've probably waited for GTX670 - it is very close in terms of speed and is significantly cheaper). I went with EVGA's version - EVGA is a very good company, with excellent warranty and very good and responsive customer support (which I had to use a couple of times before). I have a regular, non-overclocked version - it was the only one easily available at the time of purchase and I don't really need extra performance from overclocking. If you want faster versions - EVGA has many different editions with guaranteed overclock, including the one with pre-mounted waterblock. They also have their own overclocking tool, called "Precision X", with a video guide
, if you're into manual overclocking.