iTunes Web Remote
In 2008, I bought a couple Airport Express modules to create an iTunes controlled whole-house-stereo. It was awesome until a terrible song would come on and I'd have to run upstairs to skip to a better tune.
Apple quickly became aware of this problem and released an iTunes remote for iOS. However, at the time I didn't have any iOS devices and I couldn't justify spending a few hundred dollars for an ipod touch/iphone music remote. As such, I decided to build a remote of my own.
Using PHP and AppleScript to communicate to iTunes, I was able to whip up a super light web-based remote that ran on my Mac. With "LAMP" running locally, I could visit the IP of my Mac from any device on my internal network and navigate my songs.
At the time, I used this to switch songs via my blackberry, sidekick, a PSP, or even our Nintendo Wii. It was great for parties!