I test a lot of iPhone apps, but because I've only got an 8GB iPhone 3G, I end up deleting most of them after a few days or weeks. One of the very few exceptions has been iConcertCal, which helps you find local shows by your favorite artists. Not only has it stayed on my iPhone since I first reviewed it in July, but it made my year-end list of most welcome digital audio products.
Now Android users can get in on the fun with iConcertCal for Android. Like the iPhone version, it will identify artists in the music library on your phone, then display them in a calendar of upcoming live shows in your area. If you install the iTunes plug-in on your computer, iConcertCal will provide a list for every artist in your iTunes library, whether you've transferred their songs to your phone. You can also see a list of all upcoming concerts in your area (it draws most of its information from JamBase, a longstanding and very accurate user-populated database), arrange listings by venue and in order of distance (if you're just looking for something to do right now), and can switch the default city in case you're planning some travel.
The Android version also has one unique feature that the iPhone version lacks: it will also show upcoming album releases by your favorite artists. It's available in the Android Marketplace now for $2.99, the same price as the iPhone app.