Hi Qarano, a good starting place would be
this article showing this site's own suggested $500 build.
If it were me, I'd go with
this PSU (Antec HGC-400W) instead, though, which is $20 more than the article's suggested PSU (Antec Earthwatts 380W). I say this because you don't want to skimp on quality when it comes to PSUs: the Earthwatts uses a mix of Taiwanese and Japanese capacitors, and you want all Japanese capacitors for optimal reliability (see
this review of the Earthwatts, I think this quote from it provides a good summary: "
Overall my impression of the internals is a bit of a mixed bag. The build quality is good with very good construction and a generous design but the double forward design is not cutting edge and the capacitor brand choice is stingy yet adequate.". (Also note that the Earthwatts doesn't come with a power cord). The Antec HCG 400 is the lowest price PSU with all-Japanese capacitors I could find and the 520W version is
reviewed well at Anandtech. In my opinion the extra $20 is worth it for the extra reliability.
Also, bear in mind that none of these builds include the cost of windows (an extra $100 minimum) if you're going that route. If you're looking to shed cost a bit more, you could go with a lower end
AMD Phenom x4 CPU or even the
Athlon x3 Rana instead of the Intel Core i3. This would save you $20-$45 compared to the Core i3 (you'd go with an AMD motherboard for about the same price, of course), but you'd lose some performance. Another option is to get a cheaper graphics card to lower cost (and upgrade later); it really depends on how much you're comfortable spending.
One final note: if you can afford it, I highly recommend a 60 or 80GB solid state drive (SSD) to boot your operating system from (and load games from), it's probably the single best upgrade you can make in terms of snappiness and load times. Thing is, upgrading to a SSD later means reinstalling windows to it to benefit most, which is a pain. It's a sweet piece of hardware if you can fit it into your budget.
Good luck
Edit: I've build a system in the NZXT Gamma and it's a solid case. The Xigmatech Asgard case in the article I linked to has also been reviewed well.