(Not that I just did a giant review of mine
Yeah, anything that has a standard headphone jack, like a CD player, a computer, or I think you can get an adapter for a guitar or keyboard, works just fine. You can even hook it up to your DS or PSP and use it while you play video games. (Though I can't guarantee you'll be very good at them while you're distracted. XD) I think with the right cord converters you could do just about anything, though it might get complicated...
They're awesome, they really are. I love mine to bits.