This is a textbook for a first computer science course for students majoring in computer science, as well as mathematics and the physical and social sciences. It is being updated regularly, and the "last modified" date at the bottom of this page is updated each time a new book revision is posted.
It's available under the GNU Free Documentation License.
The book, in pdf format.
The source code, tar'ed and gzipped. Makefile included. Requires LaTeX and fig2dev.