As glued to the net as we all are, there's vast quantities of content that is not available online.
We've known for some time already that Amazon's AZW files are actually Mobi files, but Amazon didn't share Kindle's Mobi PID which would allow one to buy encrypted Mobi books for Kindle.
Use Mobipocket software to convert PDFs to that format so you can read them on Kindle.
Non-DRM Mobi books, like free e-books found online in Mobi format, or files you convert to Mobi files, are already supported 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.