Free site that teaches you all about electronic circuits, and how they work.

http://www.allaboutcircuits.com/education/

Electronics Textbook
This site provides a series of online textbooks covering electricity and electronics. The information provided is great for both students and hobbyists who are looking to expand their knowledge in this field. These textbooks were written by Tony R. Kuphaldt and released under the Design Science License.

Video Lectures
Thanks to a contribution to AAC from Tim Fiegenbaum, we have over 100 Video Lectures based on the textbook "Electronics for Computer Technology". These video lectures cover many of the topics contained within the textbooks, and are an excellent supplement to reinforce concepts.

Worksheets - Test Your Knowledge
The worksheets were created by Tony R. Kuphaldt, and contain hundreds of categorized questions and answers. They provide a great way to test your knowledge and prepare for exams.