Dorai Sitaram's online Scheme tutorial, Teach Yourself Scheme in Fixnum Days, at http://www.cs.rice.edu/~dorai/t-y-scheme/t-y-scheme.html. Includes a nice explanation of continuations.
http://wombat.doc.ic.ac.uk/foldoc/.
The complete text of Structure and Interpretation of Computer Programs, the classic introduction to computer science and Scheme by Hal Abelson, Jerry Sussman and Julie Sussman, is now available online at http://mitpress.mit.edu/sicp/sicp.html. This site also provides teaching materials related to the book, and all the source code used in the book, in a form suitable for loading and running.

Further Reading