Songkick

Songkick aims to be the home of live music on the web.

Songkick is a concert listings site that has created a comprehensive database that tracks concerts as they appear on 16 different ticketing sites in the UK and the USA and across dozens of blogs. You can search the database and track shows and blog posts about your favorite acts, or download SongKicker, which automatically tracks artists you listen to.
SongKicker is a plug-in that pulls artists you listen to from iTunes, Windows Media Player, and Winamp.

Songkick makes going to shows as easy as going to the movies.

More listings are constantly being added to ensure that every single concert in existence—no matter how obscure the band or tiny the venue is listed. Songkick even index bands' MySpace pages to make sure they have all their dates.