The AppleScript Sourcebook includes an AppleScript tutorial, updated to Mac OS X 10.2.

MacScripter.net is a collection of AppleScripts, useful at least as a bunch of working examples.

Apple's own AppleScript site includes official documentation, and descriptions of example scripts for a bunch of Apple applications, some already on your hard drive and others available for download.

Overall, AppleScript: The Definitive Guide appears to be one of the best introductions to the language. It's quite readable, though there's so much discussion I'm not interested in that, for me, the book could be about half as long and contain as much useful information. I made the mistake of buying it in a brick-and-mortar bookstore for full price ($40); Amazon sells it for $16.