Beware the Kindle Leather Covers from Amazon
When I bought my wife a Kindle, I also purchased one of the Amazon Kindle Leather Covers specifically for the device. She attached the Kindle into the case per the instructions and two days later, her screen cracked from the inside. Amazon quickly replaced the Kindle. When the new one arrived, we attached it into the Kindle Sleeve case and it cracked as well.
Checking online, we discovered that the cases that Amazon sold specifically for their Kindle product caused pressure on the screens, even though the attachments were clearly marked on the Kindle itself, and the case is what caused the screen to crack. By this time, we were on our third Kindle and returned the case for a full refund as well.
When looking at these cases, beware those with the custom hinges that lock the Kindle into place. The reason for the cracks is that the cover is meant to be opened from the front, but if it is accidentally opened from the back, it cracks the device. Being careful with the product will protect it, but a case made for a specific product and sold by the company who promotes it should be safer.
The Kindle case we purchased was the Kindle Leather Cover, which runs $19.99 through Amazon.com as of April 2011, a nice price but not worth the trouble of having to replace your Kindle in case of incidental cracks.