Many of the media types here in LA swear by the HP z800 workstation. It is super quiet. The innards are designed by BMW. Quad Core Processor with up to 3.3htz processors and 32g of RAM. You can also order a second processor! It supports 6 SATA drives internally with RAID 0 and RAID 1 native to the motherboard, e.g., no controller card necessary. Comes with a 1gig network card, but you can add a second. Video Card Supports two DVI Monitors natively. It has a ton of USB 2 I/Os right to the motherboard and also 2 firewires right to the mother board. So no IRQ issues.
I just bought one and it is a friggin rocket ship. The only complaint I have is that I hate HP Video Cards, with the proprietary "display" plug. I would order a different adapter, like a Display > VGA adapter from HP, or junk the Video Card altogether. Also, it has no PCI cards slots, only PCIe.