Enermax, Topower, Sparkle (Fortran, Aopen), Antec, PC Power and Cooling,Enlight, Some Seventeam, HighPower and Enhance Psus - make up many of the best(among others) PSus around.
In terms of features (extra molex connectors, noise, temp monitoring) then Enermaxes, Topowers and PC Power and cooling will often come out on top- but in terms of just being a 'good PSu' all of these brands do the job well.
GreyWolfe- You need to tell us more about what this PSu will do? If you are powering numerous devices, or a dual MP system you might really need that 500W, however if you are wanting it to O/C an Athlon- you may want to look more at the output down the combined 5v and 3.3 rails
here is a very basic leadman 500W review