Help, Broke a cap off my ipod

You'll have to use a cap meter.  All you can tell by looking at it is that it's a ceramic cap, not its value.

You probably don't have to worry about voltage rating.  Once you know the value, I'd just get whatever X7R fits that footprint.  It's hard to judge scale from that pic, but it looks like an 0603 size cap.  If you have some calipers, post the measurements, or just compare them to the measurements in the datasheet for the cap you're looking at.

There's a chance the iPod will still work without that cap.  Have you tried it?

Maybe, might not be accurate though. Have a friend with a similar iPod that wouldn't mind you opening it up?

Or maybe you can find a broken one on eBay for a few bucks.

Loss of one little ol' ceramic shouldn't cause that.  Are you sure the event that knocked this cap off didn't cause other damage?  A cracked trace maybe?

That's most likely what it is, statistically speaking.  I'm basing that on an assumption that decoupling (a.k.a. bypass) is the most common use of ceramic caps.  I could be wrong, or your iPod could be an atypical user of ceramic caps.

A well-engnineered system is designed so that every last decoupling cap isn't absolutely required for the device to function at all.  You want to overengineer things a bit, for lots of reasons, not just the unlikely possibility that one will be knocked off the board.  Apple knows how to do proper engineering.  

If instead your iPod started but crashed shortly after startup, that'd be different.  I'm not saying the cap is pointless so removing it is totally harmless, just that there are reasons why removing it should not be expected to completely brick the iPod.

I doubt it.  Coupling caps are an analog filtering type function.  Failure to boot is a digital-domain problem, which is all about DC.  There shouldn't be any coupling caps in that section of the circuit.

A much better theory, though probably less statistically likely than mine.

I don't see any need to tie it directly to the HDD.  It could be a filtering cap for the DC-DC converter that turns the 5 V USB power into something more like 3.3 V for the main processor, for example.  Losing that could certainly kill the device.