I finally understand how transistors work! Electricity in general has been a blind spot in my education, but what principles I thought I understood were completely violated by transistors, often as described in the same books.
As it turns out, transistors are not some weird three-legged circuit powered by one battery, and there's no positive charge magically pushed to the end of a wire (presumably expelled from the tank of compressed hydrogen nuclei found in all computers).
Transistors are circuits — two of 'em in fact, each with its own power source just as you'd expect. Sure, there's three physical wires, but that's because charges flow in through one wire, and then leave on two different wires.
Transistors were never all that weird, they were just explained badly. I think that if your textbook had images like the ones above, you learned how they really work only by chance, if at all.
PS: Beaty also has an “excessively short” version of the transistors article, but I don't recommend it. Too much new covered in too little time.
Update Sun 25 Jul 2010: Another great find: “Why Three Prongs?”. If you never understood why (or how) a circuit might use a third wire, this is the clearest explanation I've ever read.