Though the iPad doesn’t have a USB port of its own, with one accessory, you can connect some USB devices – like keyboards and headsets – to the iPad. That accessory is Apple’s iPad Camera Connection Kit, which offers a USB adapter that plugs into the dock connector.
With this, you can plug some USB devices into the iPad. Not all accessories seem to work with this trick, so it may require some trial and error, but both keyboards and headsets have been shown to work.
So, if you’re willing to spend the US$29 Apple charges for the Camera Connection Kit, you can unlock a world of unofficial iPad accessories.