Amazon has offered a free ebook conversion service for as long as they have sold the Kindle. Simply email them a compatible file and they will convert it for you and add it to the personal docs section of your Kindle account.
This service is one of the many reasons the Kindle is so much easier to use than its competitors, but it still has a caveat: Amazon won't accept an epub ebook.
Now one MobileRead user has found a new trick to get past Amazon's filter.
They found that you can change the suffix of the epub ebook from EPUB to PNG and email it to Amazon, and the ebook will be converted to Kindle format for you.
This has been tested by a number of users on MobileRead, and they have confirmed that it works.
I keep my ebooks in calibre, so i don't find this terribly useful, but I wanted to share it anyway.
If you keep your ebook library in your Kindle account then this will save you a fair amount of work.
P.S. When it comes to the Kindle conversion service, the only supported formats are: PRC, Mobi, PDF, Doc, Docx, txt, rtf, and image formats (gif, bmp, png, jpeg).
The restriction makes sense, but it has frustrated users and forced them to come up with workarounds. For example, there are services that will email your epub ebooks to your Kindle account. Also, if you change the an epub ebook's suffix from EPUB to ZIP, Amazon will accept it for conversion.
image by René Clausen Nielsen