Am I the only one who noticed that the OP didn't post at all about the uses of his computer? For all we know he could be wanting to build a web server.
xenongfx, we need you to post any and all uses of the computer (basics, video editing, youtube, gaming, rendering etc), and what monitor resolution you have. This last part is important if you are gaming. Also, if you are gaming, please specify the games.
Further questions:
-Any overclocking plans?
-How important is overall size / quietness?
-Do you have an brand preferences or any other preferences you haven't mentioned?
-How long do you want to keep the computer for your uses?
-Do you need an OS to be included in that $500 pricepoint?
-How much hard drive space do you need?
So far overall, I think you are looking at a cheap OCZ/corsair/antec earthwatts PSU with an Athlon IIx3. Add in a radeon 5750 or 5770 if you plan on gaming. I recommend the 1TB WD black hard drive for good bang/buck. The 640GB black is a good alternative. Ram should be 4GB these days in general but if on a really tight budget, 2GB can just get you by. Case is a rather personal preference and pretty much anything should be able to keep things cool in your pricerange. I've owned an Antec 300 and an In-win dragon slayer. both seem solid budget cases. the in win only supports mATX size motherboards though. The in win is quieter and smaller but the antec is less expensive and is kind of a standard "budget build" case because of size, cooling capabilities and build quality. I did notice that the antec had a crappy front headphone jack that led to a lot of hiss. With the same motherboard, my in win doesnt have this issue and I've started using the front again. Although it could have simply been my lack of cable management in the antec 300.