CPU: Intel Core i5-2310
$189.99 (before $10 off w/ promo code EMCJHHK26, ends 12/26)
Mobo: MSI H61M-P21
RAM: PNY Optima 8GB (2 x 4GB) DDR3 1333
HDD: HITACHI 500GB 7200 RPM
Case: GIGABYTE GZ-F2HEB
PSU: Antec EarthWatts Green 380W 80+ Bronze
DVD: LITE-ON DVD Burner
Total: $448.93 after $9.00 shipping and $10 promo code (before $15.00 mail-in-rebates).
You won't be able to fit a fast GPU into your budget. You can't fit most of your requirements into your budget. You could step down from the i5 to this i3-2120
and come in at $388.93 (after shipping, before rebates) without a GPU, though. You can always add a GPU later if needed, but since you're using Linux, I'm assuming you won't be gaming, and therefore the onboard video should be fine.
If you give me some more information to go off, for example what you're using your computer for (instead of just needing it to be "fast"), I can probably give you some better advice.