You're right, PSUs that are supplied with cases are usually pretty crappy. There is one exception that I know of, the
Antec Sonata III. It comes with an Antec 500w Earthwatts PSU, which is a decent power supply. If you don't already have a case, and you still want a combo deal with a PSU, then that is a good choice.
As far as separate PSUs go, Corsair is the best brand right now, I believe. If you can find some from PC Power and Cooling, they are pretty good as well (although I think they were recently bought out by another company, OCZ I think). There are other brands, but I can't remember them all. Go
here to look at the PSU tier list. It shows what PSUs are good, and what ones aren't. It's on the second post of the page.
Also, as for how many watts you need, I'm not sure. Given the information I see now, I'd like to say that 500w would be okay. But who knows if you want to add more hard drives, fans, or anything else that needs more power. Check out
this site for a PSU calculator. You can enter in all the components you are planning on, and even add in some things that you may buy in the future. It will give you an estimate of how large a PSU you need. Overkill can be good, as long as you don't go overboard. For instance, the calculator estimated that I would need about 480w for my build. I decided to get a 600w supply, just to make sure I have enough headroom. Besides, the price difference between a 500w and 600w is pretty small.
Athlon X2 5000 BE 3.1GHz, Arctic Cooling Freezer 64 Pro, Gigabyte GA-MA770-DS3 AM2+, Visiontek HD4850, Corsair XMS2 2GB DDR2 800, OCZ StealthXStream 600W PSU
