The Promise SmartStor DS4300 is a RAID drive with one-touch configuration to set up new drives in the device and a direct plug for your computer. The Network Attached Storage Device (NAS) can host both USB 2.0 and eSATA drives and hooks into your existing network through an ethernet cable.
The Promise SmartStor DS4300 will be available in May 2009 for around $400. If you need something a little more heavy duty the DS4300 was announced alongside the NS4600 which also works as a media server.