dotEPUB

You can write your text in Markdown format and dotEPUB will convert your text into an e-book (ePUB or MOBI format) that you can read on an iPad (iBooks) or the Amazon Kindle.

dotEPUB is available as a bookmarklet and as a Google Chrome extension allowing you to convert just about any web page into an EPUB or MOBI format ebook.

Also, if you would like to convert a Word document or a PDF file to EPUB / MOBI, just upload the .doc or .docx file to Google Docs and then use the dotEPUB bookmarklet to convert it into the appropriate ebook format.