AppEngine is pretty cool
Free hosting for webapps... python or Java, sweet.
Thrown up two apps already
android remote control console, find your phone, download files or run scripts!
quick and easy screen shots straight from a webpage; drag and drop, paste or capture straight from your screen
I have another app that's used to track my passifox Firefox extension installs (user count and browser version) that takes only a few hundred lines. Delightful.