A bit too early to give any links. Start looking at specific candidates maybe 1 week early. Of course it'll be good to have some idea of what sort of a setup you're aiming for, so here's what I'd want in a $500 1080p gaming PC
- ATX case that can take a long graphics card
- Decent quality PSU that can take a GPU upgrade
- At least 7750 or 7770
- Ivy Bridge Pentium CPU or better, or AMD quad core
Since you already have an operating system, you should really consider just buying the parts yourself and building it yourself. It's not that difficult, and you get to pick a lot better components than you'll ever find in a $500 OEM rig