Recommendations for a Single Board Computer?

Lardmonster asks: "I'm looking for a Single Board Computer that's reasonably spec'd for performance, but low power (from a Wattage perspective!). I'd like to build a small machine to host NFS/Samba shares, store email, and run Slimserver. There are some nice-looking boards from Soekris, but they max out at 266MHz and have limited RAM. Can anyone recommend similar devices that are low-power, up to 500MHz, with IDE connector and have a SO-DIMM slot? Compatibility with i386 binaries is not necessary. Many places sell similar boards, but only in large quantities, and the prices are generally prohibitively high when they're publicized at all."