The iPad Orchestra (http://vimeo.com/14551679)
The iPad is gaining a solid reputation as a musician's infinite instrument, and nothing demonstrates this better than this video of The iPad Orchestra by Alex Shpil.
Four musicians, all using the Seline HD (http://itunes.apple.com/us/app/seline-hd-music-instrument/id388640430?mt=8) app on amplified iPads, play a piece called "Sweet Dream" composed by Ilya Plavunov. The quartet consists of cello, flute, violin, and clarinet. The result is... magical.