There are serial cables/cradles available too, which open up a world of low-level hardware fun.

Things that old Palms are useful for, now that they're essentially free:

• Universal IR remote controls
  
• Replacements for character/graphic LCDs
  
• Handheld MIDI controllers
  
• Bike computers
  
• GPS
  
• Microcontroller substitute

You get a cheap, programmable computer with a display and user input. With a bit of imagination and research, and serial I/O to the outside world, they have a thousand uses.

Best of all - they're 68ks }