Which psu to choose?

For a single card set up
Any of the below - 500-550W would suffice, but IMO 600W is a safe bet just incase you upgrade later on as PSUs can be reused for later builds as well.
Corsair 600W Modular - Very good for cable management inside the case also less clutter.
http://www.newegg.com/Product/Product.aspx?Item=N82E16817139048

Seasonic S12II 620
http://www.newegg.com/Product/Product.aspx?Item=N82E16817151096

If you count in rebates, this is a very good option - Modular and cheaper when counting in rebates
Antec HCG M Series HCG-620M 620W
http://www.newegg.com/Product/Product.aspx?Item=N82E16817371059

For multi-card setup, you would need to go higher.