KB6NU's No-Nonsense No-Code Study Guides Concise and clear Study Guides for every test.
Shenandoah Software - Free Amateur Radio Practice Testing Software!
W5JCK's Extra test Math Guide. The best free Extra Test Math study guide on the web.
ARRL-VEC ARRL's Amateur Exam Question Pool
W9PE's Ham Cram Power Point Presentation for the Technician's License
Study Guides by N8KBR Study Guides for all Amateur Radio Tests
HamTestOnline.com The site is not free but I have heard very good things about it.