Recommend size is 600w for the card, so anything 600w or higher is good. Ideally you would want something that says 'modular' in the title meaning that every cable can be removed from the thing which helps in installation. There is also a rating system for the performance of the power supply (bronze,silver,gold) but most of that just means you will save a few pennies a year on your electricity bill so it isn't really a big factor.
Seasonic is pretty much the best brand you can get and a few other companies still use seasonic for their PSUs (corsair uses them and I believe a few others).