The important way to select a PSU is by looking at the ratings on the +3.3v and +5v lines. I have a generic-ish 400W PSU and it delivers about the same power as a brand name 300 or 350W unit I think.
The general rule I've heard is to multiply the volts by the amp rating for the 3.3v and 5v lines(example: 15A on the 3.3V line = 49.5 and 20A on the 5v line = 100) and add them together, there should be a minimum of 200 (I heard this was the PSU guideline for an Epox 8K7A)
So look at the PSU's ratings. Otherwise, if you want to buy by brand name, Antec's, Powmax, Enermax are all good brands if you get 300W or higher.