Electronics retailer Gazelle has been calculating up the various values of used electronics, and the firm has found that the iPad will hold its value way better than the Amazon Kindle has so far. The Kindle e-readers have only held, at the most, about 33% of their price after a year of use, while the iPad is usually sold for about 50% of its original price. Even the iPhone is more valuable after it's used: Old iPhones are selling for about 40% of their original price.
It's no surprise why: Apple products are continuing to remain in demand even after they're updated, and the Kindle's lower price and fewer features probably doesn't help the resale value either. If there's a not a big difference between the used and new prices and not many new features, why wouldn't you just buy a new Kindle? Obviously the iPad 2 is faster and has that camera, but an original iPad is still very useful, making it much more valuable for the price.
All of that said, of course, this tablet market is changing very quickly, and the pattern that we've seen with the iPhone is that as more models come out, the earliest models are worth even less; just find an original iPhone on Craiglist these days to see how cheap they can be now that the 4 and 4S are out. With another iteration of the iPad expected out this year, we might see the earliest models become quite cheap on the resale scale.