This is a great website that offers all the resources you need to grow professionally. It has different sections with each one full of PDFs, books, articles an many more .
2- Discovery Education
3- Staff Develop
4- Ed Week
Ed Week is a also one of the leading websites in education. It helps teachers and educators grow professionally by providing all kinds of resources for free.
5- Educators Professional Development
6- Read Write Think
7- Teacher Vision
8- Teachers Domain
9- Getting Smart
10- Common Sense Media
CSM is dedicated to improving the lives of students and educators by providing some great resources, information, education, and independent voice they need to thrive in a world of media and technology.
11- Teacher Trap
12- Teachers Network
13- Intel Teach Elements
This is a free professional development platform from Intel that provides a series of compelling courses on the 21st century learning concepts.