http://www.upscale.utoronto.ca/GeneralInterest/GeneralInterest.html
Basic circuit theory as part of an extensive Physics site.
http://www.gcse.com/electricity.htm
A collection of real-time, theory-based interactive simulations of some simple electronic circuits. (For Macintosh.)
http://www.inform.umd.edu/EdRes/Topic/Chemistry/ChemConference/Software/ElectroSim
Eliminates noise on long leads.
http://www.uoguelph.ca/~antoon/gadgets/noiserx.htm
A really slick design guide for all sorts of filters. Includes DSP filters.
http://www.freqdev.com/guide/index.html
Course designed for high school science students.
http://www.hkstar.com/~hkiedsci
http://www.uoguelph.ca/~antoon/circ/etemp.htm
Automotive circuit
http://www.citycom.gr/electronics/downcircuits/106.zip