The thing I keep coming back to with my own PSU searching is looking at the +12v amp rating. When you've identified every other PC part you want, take a look at the power requirements of the biggest power draw (usually the GPU). That will let you know what size PSU to get. If you can't find the amp spec for a PSU, I'd skip it.
Newegg has been having some great sales on top quality PSU's for months, especially in the 550-750W range.
What you don't want to do is buy a PSU that turns out to be inadequate for three reasons.
1. It may work but with a shortened life.
2. It will pick an inopportune moment to die.
3. When (not if) it dies, it is more likely to take another component(s) down with it.
Good luck!