A NAS (Network Attached Storage) unit is basically a hard drive connected to the LAN. Many NAS units run a form of embedded Linux, which opens a whole world of hacks and tweaks :)
The Matrox Shared Storage (MSS) has a 300Gb hard drive . With the alternative firmware "OpenMSS" (See resources) you can easily enable a NFS and OpenSSH server. The MSS is connected to the LAN via 100Mbps ethernet. Furthermore the MSS has 2 USB ports that lets you connect external USB hard drives or other USB storage devices.