One of the best resources for CS notes, PDFs and presentations are the homepages of Profs at various IITs. Each professor at IIT has his own homepage where he lists the courses he is teaching, and has taught in the past. Invariably, they also have links to course materials, reference texts, assignments and their solutions and some very interesting links that can be very helpful for someone trying to understand the subject.
Just enter the subject you are interested to learn about. E.g. enter "Discrete Mathematics" in the search engine below and see the wealth of resources returned. Happy learning.