There are two types of data transfer cables most consumers are familiar with: USB and FireWire.  Apple's iPod took advantage of both and even though the USB cable won out, some of the older generation iPods work with FireWire still.  These FireWire cables offer higher data transfer speed, quicker charging for the unit and an overall smoother process when hooked up to a computer.  While USB is compliant when it comes to data transfer now and will no doubt eventually be developed down the line, for now it is the primary way to use new iPods.  If you have an older generation iPod, you may be able to use FireWire cables to make things a little bit quicker.

The Apple iPod FireWire cable only works with iPods generations one through four, generations five and up do not support FireWire, only USB cables.  Many consumers opt to use FireWire strictly for charging the unit, as it can be done a bit quicker with it than with the standard USB cables.  The FireWire plugs into a compatible computer or socket, then into the iPod.  From there, it charges or transfers data depending on what you want to do with the MP3 player.  It basically does the same thing the USB cable does except through a higher data transfer port.  Many computer come with a single FireWire cable port nowadays.

Apple offers a FireWire cable for the iPod, although it is much harder to get a hold of nowadays.  Even Apple's web site store does not carry it.  You have to find it via a third party vendor or retailer online.  Unless you are looking for a FireWire cable specifically, you are better of sticking with the USB cable as your standard.  Otherwise, you may have a bit of trouble finding a FireWire cable compatible with your iPod.