Collection of Terence Tao's blog posts (terrytao.wordpress.com)

Direct link to the PDF: http://terrytao.files.wordpress.com/2012/11/blog-book.pdf

Older collections:

1. http://terrytao.wordpress.com/books/whats-new-2007/

2. http://terrytao.wordpress.com/books/poincares-legacies-cours...

3. http://terrytao.wordpress.com/books/an-epsilon-of-room-pages...

4. http://terrytao.wordpress.com/books/compactness-and-contradi...

5. http://terrytao.wordpress.com/books/hilberts-fifth-problem-a...

The downloadable versions are labelled "drafts" but are of very high quality.