AMD last week announced the availability of a couple of desktop A-series quad-core APUs -- A6-3650 and A8-3850 -- both of which are now offered in CyberPower's gaming PC lineup. These Llano parts are the main attraction in CyberPower's Gamer Ultra desktop line, and you can pick up a full blown setup for as little as $595.
You're not going to build a supercomputer for under $600, but the Gamer Ultra 7000 Elite does come with the following:
CoolerMaster Elite 430 mid-tower case
AMD A6-3650 APU (2.6GHz, Radeon HD 6530D)
Radeon HD 6450 discrete graphics card
Asetek 510LC all-in-one liquid cooling system
MSI A75MA-G55 motherboard
1TB SATA III hard drive
24X DVD burner
Speakers / Keyboard / Mouse
Windows 7 Home Premium 64-bit (w/ $50 mail-in-rebate)
430W power supply
A respectable machine for a daily workhorse, though if your budget allows, it could use a handful of upgrades to really be considered a gaming rig, starting with the discrete graphics card. There are a ton of configuration options available, and a whole bunch of post July 4th promotions, which you can check out here.