I can't remember all the details, but it's a Core i7 920, with 12GB RAM in triple-channel mode. There's a mid-range nVidia graphics card (I'm not a gamer) and a PCIe-based SSD (so it's more than 4 times quicker than a normal SSD). There are five other hard drives -- nearly all Western Digital.
I was going to overclock it, so it has a liquid-cooled CPU block, but I never bothered in the end. It's fast enough, and I value rock-solid reliability more than a little speed boost.
It used to triple-boot XP, Windows 7 and Arch Linux, but I got rid of XP and run that in a virtual machine now.
It's over 8 years old now, but it's still really fast. It should last another 4 years or so, at least. All-in-all, great value for money and great performance. I'm pretty happy with it.
When it comes time to upgrade, I'll just need a motherboard, chip and RAM, so it will be cheap to upgrade too.