GreenFoot is free, open-source software which is good for very young learners.
http://www.greenfoot.org/
BlueJ is free, open-source software which is good for intermediate learners.
http://www.bluej.org/
"Barron's AP Computer Science..." book is a good introduction. The link below is a good book that is available inexpensively because the AP Exam is only available now for AP Computer Science A, and the AP Computer Science, level AB has been discontinued for college-credit, but this book is still available and covers both level A and level AB.
http://www.amazon.com/Barrons-AP-Computer-Science-Levels/dp/0764137093/ref=sr_1_1?ie=UTF8&s=books&qid=1250639829&sr=8-1
Eclipse is free, open-source software which is good for advanced learners and for professional software engineers.
http://www.eclipse.org/
Here is a link to the Computer Science Teacher's Association:
http://www.csta.acm.org/
I hope that this information helps you.
-- Kaydell