Anything 500W+ with two PCIe connectors and is produced by a decent manufacturer.
Corsair, Antec, or OCZ usually have some good value options.
A few examples to get you started:http://www.newegg.com/Product/Product.aspx?Item=N82E16817139027 http://www.newegg.com/Product/Product.aspx?Item=N82E16817371035
Im not from the US but these are good PSU's for your setup, something along these lines or better will work well for you. Best to dig around for the best prices though
Edit: Didnt think to check if the PSU you already have would be suitable, should be alright but youll want to make sure you have 2 PCIe connections. Not a big fan of using molex adapters!