1- The Complete Works of William Shakespeare:
Here, you can find all the works of William Shakespeare. It's really amazing. You can read all of his work for free.
2-Open Yale courses:
In this website you can watch videos of lectures given by distinguished yale professors for free!
This is a very helpful website for the students. Enjoy :)
3-Standford's University Documents search:
There are about online documents in this website. It is a very useful tool for research.