iConcertCal - So obvious, and pretty useful...

iConcertCal is a program that works with iTunes to find upcoming concerts in your area by artists that you like, based on which artists are represented in your song library. It was originally an iTunes plugin, and is now an iPhone app as well (iTunes store link) - and provides useful features like direct links to purchase tickets, venue maps, and more. It's really quite obvious, just plain genius - and a very, very usable design!
[via Gizmodo]