I started playing with the Songkick APIs a couple of weeks ago. Songkick is a lovely service I've been using for a couple of years, that tells you when your favourite artists are touring nearby. In much the same way as Nike+ and Kindle, it's made a big difference to my life by stimulating a specific behaviour: getting out to see live music.
The API lets you query their mahoosive database of gigs and artists fairly simply - I've open-sourced a Java library which I've written to access their REST API, and wanted to use it on a Real Project to prove to myself that it actually worked for something useful.
I've rarely gone to gigs by myself. It's always been a social experience for me, and nowadays in my late 30s I quite enjoy catching up with an old friend by heading out to see someone from Our Youth play live. A couple of long journeys and a lazy Saturday in Barcelona gave me a chance to finish SongkickFor2, a little web app which helps you find a gig to go to with a friend. It's pretty simple: tap in your and your friends' Songkick usernames, and get back a list of upcoming concerts you both might like. I link through to the Songkick pages for these concerts, where you can buy tickets.