Someone was asking tonight about power supplies. As I mentioned at the time, I think Enermax is the most reliable. I've sold over 2000 Enermax PS's over 10 years and it is by far the one that dies the least often. I've done at most 2-3 repairs/replacements of Enermax PS's. The rest are still running. Everytime I give another brand a try, I regret it.
The only other brand I consider is if I need to "cheap out" I'll use an Antec case with a builtin Antec PS. They seem pretty good too and are more affordable (when bought in the case).
In either case, I recommend the APFC models, as they save electricity (lower TCO) and are generally built better.
My favorite model for Enermax is the Liberty series and I use the 400 and 500W's successfully in nearly all computers. A good 500W will give you more and cleaner power than a cheapo 600W.
My company sells them if you have trouble getting them elsewhere or want to buy local. Email me for details/pricing. I can bring orders to the meetings.
Good luck!