I couldn't show you a computer that I would say, "This is what you need" because at that low of a price, it depends a lot on what you're doing.
If you're gaming, you'll want a lower end CPU and RAM, and go for a good Video Card.
If you're doing photo or movie editing, the CPU and RAM are going to be more important.
I have made several setups on cyberpowerpc.com that were under $700 if I went with AMD, but then again, that is normally considered a lower end company that Intel.