I'm in the process of publishing my second eBook for the Amazon Kindle, and one thing that's currently hard to find on the Amazon website is what the eBook cover height and width size specifications are. You can currently only find this information when you get ready to publish your book.
So, as a brief public service, as of May, 2012, here are the Amazon Kindle eBook cover height and width specifications, courtesy of the Amazon KDP book publication website:
Update: As you can see from this new image, Amazon now has a link to their Product Image Guidelines page, which now shows this same information. This information wasn't available when I published my first eBook.