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 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.
Thanks to Toyo for the tip!