Rui Carmo- The Linksys NSLU2 Network Storage Server - It serves USB storage over SMB, but be warned: you cannot swap disks with PCs (I wonder if it uses ext2 as a filesystem) and there is no mention of accented character support in filenames (a common issue when you have SMB and wildly varying language configurations). Check the User Manual (PDF) - you have to read through most of it to pick up the limitations, but it actually looks pretty damn good...
- A Gmail to POP3 proxy (I'd vastly prefer IMAP access to the mailbox store...)
- Changing the Stickies .nib files to unlock all sorts of neat features
- Highlighting messages based on UUID in Mail.app - a nice way to flag your own messages in convoluted threads.
- Mixed authentication in Wi-Fi networks (both 802.1X and browser-based).