SICP

Structure and Interpretation of Computer Programs

You come in with a mind full of mush,
and you leave thinking like a computer scientist.

The famous Wizard Book by Harold Abelson and Gerald Jay Sussman with Julie Sussman. The text of this book is available for free:

There's a pdf here. There should also be a copy at archive.org.

HTML (official) http://mitpress.mit.edu/sicp/
PDF http://deptinfo.unice.fr/~roy/sicp.pdf
PDF with vector graphics http://sicpebook.wordpress.com/
Texinfo http://www.neilvandyke.org/sicp-texi/

A series of video lectures taught by two of the authors is also available for free, filmed at Hewlett-Packard in July 1986.

Another set of video lectures at Ars Digita University.

A torrent for the lectures http://www.ciz.fi/~oherrala/sicp-lecture-videos.torrent