State-of-the-art music processing/analysis technology developers, zplane, have released a unique and useful piece of software for analyzing songs.
deCoda can detect the key, tempo and chords of a song, as well as break it down into sections. In addition to this, there are a number of incredibly useful features for the musician who wishes to learn, practice or just analyze a piece of music. These include instant transposition to any key, changing of tempo without affecting pitch and the ability to isolate parts of the music by EQ so you can fill the gaps with your own performance.
The interface usefully displays melody information on a piano roll and you can even export to MIDI.
deCoda is available from zplane and resellers with a 40% discount ($32) until February 3rd