What is it you are wanting to do with your system. 450 to 550w is going to be sufficient for a great number of single card systems. I would figure out all the rest of your components first, then match it with an appropriate psu.
I plan on gettin an ivy bridge when they drop putting in at least a 560 or a 570 video card or better depending on the money i have at the time 16gigs of ram cuz its cheap. I plan on gaming on it.
corsair tx or xfx 650w is enough for your system(560-570).