Prince? He could play at least 27 instruments. On his debut album For You, released when he was 20, Prince is said to have played every single instrument: 27 in all.
Stevie Wonder? He plays the piano, synthesizer, harmonica, congas, drums, bongos, organ, melodica and Clavinet. In his childhood, he was best known for his harmonica work, but today he is better known for his keyboard skills and vocal ability. And he's blind!