I was just reading Andy Ihnatko's blog and he pointed out that the $29 Camera Connection Kit (so you can load photos directly onto your iPad without having to sync with your computer) allows multiple other USB devices to work with your iPad. Basically, it's just an attachable USB port.
For example, I plugged in my headset, loaded on a free voice recording app and recorded audio content.
What other ideas do you have?
I should also point out, I was online with an Apple tech guy yesterday, and asked if the iPad would have printing capability anytime soon. While it's not native, he did tell me there are several apps you can buy that allow you to print from the iPad (or iPhone).