you probably want upwards of 500w PSU but the key thing to look at is the rails, +12v, +5v, and the +3.3v
The +12v in particular I'd say you'd want ATLEAST 20a on it. Generally if the +12v is 20a or more then the other two rails will be plenty hitting 35-40a on either.
The ultra 500w X-Connect PSU is awesome and has 35a on the +12v rail, plus it's nice looking, and whatever cables you don't need, you don't have to plug them in, hence the name X-connect
But it costs $100, not sure if you want to pay that much. There are some other cheaper brands with decent rails like Rosewill PSU.