I recently found out that there were "jailbreaking" tools for the Kindle which allow you to apply a number of different hacks. The one that I found most appealing was the ability to add your own screen savers. Having jailbroken my iPhones before, I was expecting it to be an involved process, but it extremely simple. Jason Fitzpatrick over at How-To Geek wrote a great article that lists all of the steps necessary to get your custom screen savers on your Kindle.
As you can see I have the Kindle 3 (Kindle Keyboard). I am currently running 3.3 software and the jailbreak files Fitzpatrick link to didn't work for my Kindle. Instead I used the files linked to on Yifan Yu's website. The screen saver hack files in Fitzpatrick's article worked great, so you can use those ones.