Non DRM Mobipocket format is already supported on the Kindle - just drag and drop.
The Kindle has many flaws, but it does allow you to read a few different non-DRM formats.
Hack let you convert encrypted Mobipocket files that were intended for another reader so that that work on Kindle.
Use Mobipocket software to convert PDFs to that format so you can read them on Kindle.
A revolutionary portable reader that wirelessly downloads books, newspapers, magazines and blogs to a crisp, high-resolution electronic paper display that looks and reads like real paper, even in bright sunlight.