I'm a big silence fan! And (at the expense of ostracizing myself), I'm also a big 4'33" and John Cage fan. My favorite use of silence, though, would have to be the clarinet solo movement of Messiaen's Quartet for the End of Time. If it's a good clarinet player, it's unreal how smoothly they transition from silence to playing a reeeeeeeeeeallly quiet note.