Are you looking for a good source of information to get started into making and hacking electric circuits? We would like to refer you to Lessons in Electric Circuits. Even if you have good knowledge of electronics, this is another tool you can use. The book is a work in progress and will have some incomplete and pending areas, but the basic theory parts to get started are all there. It has six volumes: DC, AC, Semiconductors, Digital, Reference, and Experiments. The DC and AC volumes are the most complete. If your eyes are already glazing over thinking you already know all of this stuff, then the most interesting volume for you may be the Experiments, which contains a number of sample circuits like transistor amplifiers and 555 timer circuits. The best part of this book it that it is free, but as with most free things, you can make it better by contributing.
Via Adafruit Industries.