XSLT 1.0 Specification - The official W3C XSLT 1.0 Specification.

XSLT FAQ - maintained by Dave Pawson.

Rescuing XSLT from Niche Status - by David Jacobs.

Five XSLT Basics - by Michael Fitzgerald author of Learning XSLT.

XFront Tutorials - provides several tutorials include XSLT 1.0.

XSL Transformations - Chapter 17 of the XML Bible 2nd Edition.