Syncfusion is one the companies providing qualified products and material to developers all over the world. I have used their components in several of my Windows Phone and Windows Store applications.
Syncfusion offer several free e-books written by talented experts who are personally selected by Syncfusion. The goal for each book is to take 500+ pages of information on topics such as ASP.NET MVC, jQuery, HTTP, etc., and condense it to about 100 pages of essentials.
Personally I recommend the updated version of their white paper “Windows 8: What It Means for Development Decisions Today and in the Future”.