Tektronix guide describing how oscilloscope works and how to take simple measurements.
http://www.tek.com/Measurement/App_Notes/XYZs/
A program to compute Air Core Mutual Inductances.
http://www.abelian.demon.co.uk/acmi/
Teaches the basics of electronics, provides related links and application notes.
http://www.techlearner.com
Collection of teaching pages for general access
http://www.ee.surrey.ac.uk/People/D.Jefferies/
Animations of Ohm's Law, Smith Charts, and impedance matching. Free online lessons.
http://www.EducatorsCorner.com/
Basic and intermediate electronics for beginners, students, teachers and science fair projects.
http://homepage.ntlworld.com/g.knott/index1.htm
Interactive simulation of an analogue oscilloscope. Requires Macromedia Shockwave.
http://www.virtual-oscilloscope.com
http://pw1.netcom.com/~t-rex/BatDetector.html