SOHO Servers

HP MediaSmart Server ex475
Microsoft's Windows Home Server is the best, easiest-to-use answer to backing up and corralling all of the disparate media files in a networked home. And delivered in this petite, relatively affordable MediaSmart Server ex745 from HP, you get plenty of storage in a well-designed hardware package. We recommend this system all the way to anyone looking to take full control of their data.
Specs: AMD Sempron (1.8 GHz), 512 MB DDR2 SDRAM, 500 GB Hot-swap, 1.8 GHz, Microsoft Windows Home Server, Server

HP ProLiant DL380 G4 - Xeon 3.4 GHz
Specs: Intel Xeon (3.4 GHz), 1 GB DDR2 SDRAM, None., 3.4 GHz, Server

HP ProLiant ML310
As long as you don't mind sorting through its hodgepodge of user guides, the ProLiant ML310 G2 will satisfy your need for a solid entry-level server.
Specs: Intel Pentium 4 (2.53 GHz), 256 MB DDR SDRAM, 40 GB Standard, 2.53 GHz, Server

HP ProLiant DL380 G3 - Rack Model
Specs: Intel Xeon (3.06 GHz), 1 GB DDR SDRAM, 18.2 GB None., 3.06 GHz, Server

HP NetServer LH3 - PII 450 MHz
Specs: Intel Pentium II (450 MHz), 128 MB SDRAM, None., 450 MHz, Preinstalled, Server

HP ProLiant DL320 G5p - Quad-Core Xeon X3210 2.13 GHz
Specs: Intel Quad-Core Xeon X3210 (2.13 GHz), 2 GB DDR2 SDRAM, 160 GB Standard, 2.13 GHz, Server