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one with good cooling, the Zotac one looks fine with the dual fans, same with Gigabyte and it's 2 fans as well.
they are mostly the same cards with different aftermarket cooling setup's. The 480 runs very hot...usually in the mid-high 90's degrees when under gaming load so you'll need a good airflow case if you get a "basic" brand 480 without a good cooler.
Zotac looks a bit chunky yes and it's a bit pricey but the coolers on it would help...check out gigabyte's homepage for info on it's 480's and see what you can find.
Your PSU is more than fine for a 480 as well so no worries on that front.
If your MOBO has SLI options then go for two gtx 460's as they easily beat down a single 480
a 480 is more than enough for most games. Depends on your screen size what you'll get.