This is not an extensive list of materials. Just materials I have used
kb6nu.com study guides
No-Nonsense Study Guides for Technician, General, Extra and much more. There is downloadable content here from which to study.
HamExam.org
Study and take practice tests
AmateurLogic’s Ham College
Although this could count more as entertainment, it certainly is educational as it is laid out in segments that support taking exams.