Linksys Network Storage Link, Turn Any USB Harddrive Into Network Storage.
While they're promoting it with Maxtor, there's nothing stopping you from using Linksys's new Network Storage Link (NSLU2) with any external USB hard drive to turn it into a network storage device (not unlike the Mirra or other backup units). Storage Link even provides passworded web-access to files and multiple users (although they don't get into the details of how multi-user sharing will work). Since the Storage Link works via RJ-45 (regular ol' Ethernet), there's nothing preventing you from attaching it to a wireless router and using it over WiFi, either (albeit at lower speeds than a wired network, of course). Even better, it sounds like you can continue to add additional USB hard drives to the device to increase storage as you go along. Not bad for $100.
Read [Linksys] [Gizmodo]