According to entropy, and thermodynamics in general, I can't recommend enough the notes [0] of prof. Zhigang Suo of Harvard. It's a new way of presenting thermodynamics and I finally get it... contrary to when I took a thermo course at university.

[0]: https://docs.google.com/document/d/10Vi8s-azYq9auysBSK3SFSWZ...

Also prof. Suo puts entropy as the main character of the "play". The other concepts (temperature, etc.) are defined from entropy.