I am currently in a thermal physics class and am using the popular standard textbook by Schroeder. But I found some of the derivations in there non-rigorous and lack good explanation. I looked for some additional references and I came across this site: http://stp.clarku.edu/notes/ which contains a full thermal physics which you can download (by H. Gould, J. Tobochnik) This book really clears a lot of the fuzzy concepts i learnt from Schroeder's book. also, the online book has a lot of simulations which is always cool to be played around with. I thought the book is very well written and in many topics much clearer and more detailed than the ones in Schroeder's book. I just would like to share this with anyone looking for a good free text.