This is what I would go with. The graphics are real decent. Integrated but equal to a low-mid range card. (Above a 5450/6450 card, about the range of a 6670 just slightly less, but not much.) Quad core, 4 memory slots for future RAM upgrades, there are slots to upgrade to a graphics card if you end up needing it, and USB 3.0 ports. I think the USB 3.0 is the most important feature for you. It allows faster transfer rates to USB 3.0 compatible jump drives and external hard drives. Trust me you will LOVE this feature. It makes a HUGE difference. Asus also makes quality components they are used by most gamers. Ask any geek 99 out of 100 will say Asus is a great way to go.
System Specs:
http://usa.asus.com/Desktop/Entertainment/CM1740/#specifications
http://www.newegg.com/Product/Product.aspx?Item=N82E16883220138
Cost w/Free Shipping $530
If you need to upgrade to a graphics card this is what I would suggest...
http://www.newegg.com/Product/Product.aspx?Item=N82E16814161403
Benefits - GDDR5 memory, DisplayPort & HDMI, no additional power needed, 7xxx Series (newest instruction sets), HIS makes quality graphic cards, good price for performance ratio.