Syncfusion has over 80 e-books free for the download. It does require that you give them your email address and contact information and they will contact you at least once (they did me anyway). However the trade off is worth it and the person who called me was very helpful and professional and not one bit pushy (as a salesman). The e-books are relatively short and to the point. The books are all roughly 100 pages long with not much fluff thrown in. The e-books are available in ePub, mobi and pdf, which I think covers all the major bases.
For an idea of what they offer I included the category list for all the books below.
While you are there you should also make sure that you register to download a trial of their control suite or their community license version of their controls suite. The Community License provides free access to all the Syncfusion products for individual developers and small businesses
For more information see the FAQ and other community license info here. I have downloaded the controls and haven’t used them in a project yet but plan to over the next several months.
Oh yeah. I should mention that the rules of eligibility for the Community license state that any individual developer or up to five users at companies with annual gross revenue below $1 million USD are eligible to use the controls in commercial applications. So it is pretty easy to figure out whether you qualify or not and I believe the idea is to make the on-road to their controls easy for people in learning mode or for start ups with little cash flow at the time of initial development.