What are some good weekend type clone projects you can build in any language, which serves as just an excuse to get your hands dirty outside of TODO's, or a credit card validation class. Do you know any canonical things to build?
Thinking of a link shortener service, or...
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.