My 2 cents:

 

Part list permalink / Part price breakdown by merchant

 

CPU: AMD Phenom II X4 955 Black 3.2GHz Quad-Core Processor ($109.99 @ Amazon)

Motherboard: MSI 870-G45 ATX AM3 Motherboard ($71.99 @ Amazon)

Memory: G.Skill NS 4GB (2 x 2GB) DDR3-1333 Memory ($25.99 @ Newegg)

Hard Drive: Samsung Spinpoint F3 1TB 3.5" 7200RPM Internal Hard Drive ($49.99 @ Newegg)

Case: NZXT Gamma Classic (Black) ATX Mid Tower Case ($35.99 @ Amazon)

Power Supply: Antec 430W ATX12V / EPS12V Power Supply ($54.99 @ Amazon)

Optical Drive: Lite-On iHDS118-04 DVD/CD Drive ($24.97 @ Newegg)

Total: $373.91

(Prices include shipping and discounts when available.)

(Generated 2011-09-20 17:21 EDT-0400)

 

Add your current graphics card. Some stuff on that list is inaccurate, ie. with a mail in rebate the CPU is cheaper at newegg, but that specific offer ends tomorrow 21/9.

 

 

It's not worth buying a new graphics card with a $400 budget, if you bump that up to $500 though it's a totally different story. Bare in mind that this is something that can be done later - you can use your current one now and then buy a new one when you get an extra ~$100.

My 2 cents:

 

Part list permalink / Part price breakdown by merchant

 

CPU: AMD Phenom II X4 955 Black 3.2GHz Quad-Core Processor ($109.99 @ Amazon)

Motherboard: MSI 870-G45 ATX AM3 Motherboard ($71.99 @ Amazon)

Memory: G.Skill NS 4GB (2 x 2GB) DDR3-1333 Memory ($25.99 @ Newegg)

Hard Drive: Samsung Spinpoint F3 1TB 3.5" 7200RPM Internal Hard Drive ($49.99 @ Newegg)

Case: NZXT Gamma Classic (Black) ATX Mid Tower Case ($35.99 @ Amazon)

Power Supply: Antec 430W ATX12V / EPS12V Power Supply ($54.99 @ Amazon)

Optical Drive: Lite-On iHDS118-04 DVD/CD Drive ($24.97 @ Newegg)

Total: $373.91

(Prices include shipping and discounts when available.)

(Generated 2011-09-20 17:21 EDT-0400)

 

 

Add your current graphics card. I can mock one up with a new one if you want.

 

I'm impressed with the build. This is all that I would personally change:

 

Case

Optical Drive

My 2 cents:

 

Part list permalink / Part price breakdown by merchant

 

CPU: AMD Phenom II X4 955 Black 3.2GHz Quad-Core Processor ($109.99 @ Amazon)

Motherboard: MSI 870-G45 ATX AM3 Motherboard ($71.99 @ Amazon)

Memory: G.Skill NS 4GB (2 x 2GB) DDR3-1333 Memory ($25.99 @ Newegg)

Hard Drive: Samsung Spinpoint F3 1TB 3.5" 7200RPM Internal Hard Drive ($49.99 @ Newegg)

Case: NZXT Gamma Classic (Black) ATX Mid Tower Case ($35.99 @ Amazon)

Power Supply: Antec 430W ATX12V / EPS12V Power Supply ($54.99 @ Amazon)

Optical Drive: Lite-On iHDS118-04 DVD/CD Drive ($24.97 @ Newegg)

Total: $373.91

(Prices include shipping and discounts when available.)

(Generated 2011-09-20 17:21 EDT-0400)

 

 

Add your current graphics card. I can mock one up with a new one if you want.

 

I'm impressed with the build. This is all that I would personally change:

 

Case

Optical Drive

I'd agree about the optical drive, but the case is sterling for the price. If you're willing to cough up some more for the 912, go ahead it's a great series - I have the HAF X and love it. It's up to OP on price really, both are good.