If you're into live music, JamBase is , with a searchable list of more than 50,000 shows in the United States. It's updated by fans, so it tends to be up-to-date and more complete than newspaper or events sites. And it's a heck of a lot easier to run a search on JamBase than it is to pick up your local weekly and look through the ads and print listings.
Now, JamBase has come to the iPhone. You could always access it through the built-in Safari Web browser, but a free app released Monday lets you enter your Zip code--or, if you allow it to use the iPhone 3G's built-in GPS tracker, it will figure out where you are automatically--and then displays a list of shows in your area for the next few days. If you've saved a list of favorite bands at the JamBase site, you can enter your username and it'll limit results to just those bands.
It's definitely a version-1 application, and thus a bit klunky--when you click on a listing, it opens the JamBase site in Safari to give you the listing details, and you can't search for particular bands directly from the app. But it's free, and nice to have if you're stranded in, say, Los Angeles for a tech conference and want to escape from the officially sanctioned parties for some authentic jazz at a club nearby.