Today I found, completely by accident I might add, a collection of free E-Book of different Microsoft Technologies.
They cover from IT PRO to Developer subjects. These E-Books are available in multiple formats (EPUB, MOBI and PDF) and in some cases in different languages. You can find the all collection here. And I did understand that they will update the list in regular basis. So bookmark the page to receive always the news E-Books.
Here are the E-Books that I definitely recommend: