Here I collect a few notes freely availabe on the Internet which I really liked.

Computer Science

1. Draft of the book Algorithms by Dasgupta, Papadimitriou, and Vazirani available at Prof. Vazirani's home page.

2. Draft of the book Computational Complexity: A Modern Approach by Arora and Barak.

3. John Preskill's lecture notes on Quantum Computing.

4. David Mermin's lecture notes on Quantum Computing.

5. Umesh Vazirani's lecture notes on Quantum Computing available from his home page.

6. Sanjeev Arora, A Theorist's Toolkit.

7. Graduate course on Algorithms by Jeff Erickson.

8. Pseudorandomness by Salil Vadhan.

Mathematics

1. Calculus by Gilbert Strang, available from MIT Open Courseware

2. Reversible Markov Chains and Random Walks on Graphs by Aldous and Fill, available from David Aldous's home page.

3. Graph Theory by Reinhard Diestel, electronic edition available from here.

Physics

1. Course on Classical Mechanics by Leonard Susskind from YouTube

2. Course on Quantum Mechanics by Leonard Susskind from YouTube

Notes (by me)

1. Proof of Yao's Minimax Principle for Montecarlo Algorithms. CSTheory StackExchange, October 2012.

2. Interactive Proofs and Arithmetization. December 2010.