Impedance - what is it and why does it do all those terrible things to you?
Dirty Tricks you might find inside some effects and amps
How It Works - a beginner's guide to understanding what electronics is about.
The best truly basic info I've found so far - Graham Knott's Electronics for Beginners
Tom Engdahl's Basic Electonics page - a massive reference page that explains components, markings, soldering and more that you've wondered about yet. Here are a few of the topics more pertinent to effects:
Component markings explained
Circuit board design and making
These sites have even more links to other sites with basic electronics info as well. Go surfin'! Next time you will be answering that beginner's question!