Hi there. This year I have bought PowerMac G4/400 (Gigabit). It has 896Mb RAM, there is a USB 2.0 PCI controller, and recently I've installed SerialATA PCI controller and 1 Tb SATA hard drive.
Mac OS X Server 10.4.11 performs great on this hardware. You can access website hosted on this great computer at http://victor3d.karelia.ru/ .