I recently bought an Airport Express, and to me, it's really the ultimate MacGyver tool for my needs. At home, I use it to extend my wireless LAN; when traveling, I use it to create a new wireless network to free me from the cords required in the typical hotel room. No hints there, obviously; that's what it was designed to do.
But what I also figured out is that I can use the USB port on the AirPort Express to charge my phone, so I can leave the iPhone's charger at home.
[robg adds: I know this hint is relatively simple ... but as someone who will admit to having traveled with both an AirPort Express and an iPhone charger, it's definitely a tip I'm going to take advantage of on my next trip. I figured if I overlooked the obvious, maybe some others have as well.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20090419053754591