Commentary by cpressey on Electronics works
Getting Started in Electronics
A classic, with lots of cartoon capacitors etc.
Phase-Locked Loops & Their Application
Circuit Simulator Applet
An online circuit simulator implemented in JavaScript (previously implemented in a Java Applet).
The GIICM
A database of pinouts for many common IC's
ALLDATASHEET.COM - Electronic Parts Datasheet Search
A database of electronic components and their datasheets
A Review of Electronics
Many tested experiments, plus theory and history. Has a section on how phase-locked loops work.