Just learnt from Professor Terence Tao’s blog that there is a new series of free math notes by the American Mathematical Society: http://www.ams.org/open-math-notes.
Many of the notes there are of exceptionally high quality (check out “A singular mathematical promenade”, by Étienne Ghys).
Welcome to AMS Open Math Notes, a repository of freely downloadable mathematical works in progress hosted by the American Mathematical Society as a service to researchers, teachers and students.
These draft works include course notes, textbooks, and research expositions in progress. They have not been published elsewhere, and, as works in progress, are subject to significant revision.
Visitors are encouraged to download and use these materials as teaching and research aids, and to send constructive comments and suggestions to the authors.
Mathtuition88 