How about: a time tracker, HN clone/basic forum, simple Google Analytics clone, a password vault/manager (did this one recently, it was a lot of fun,
https://github.com/rfunduk/mrpassword).
Or how about some supporting type stuff: app error handling, a recommendation engine for your framework of choice, maybe a simple admin panel for doing support (using Postmark Inbound or some-such).
If you're into web stuff, it's always a good exercise to re-implement some complex plugin in a simpler way. I made a simple 'tour' plugin that a lot of people like (jQuery-TourBus), or you could make a simple carousel plugin, or maybe just make a simple sticky feedback popup thing, etc.
