This is a very cool little app that I found after listening to Security Now Episode 233: Let's Design a Computer. Some of the basic circuits were hard to visualize and this app kind of brings them to life with animated current flow and some interactivity. For the podcast you'll want to look in the Circuits menu for the Logic Families/RTL for the circuits being discussed.
This java applet is an electronic circuit simulator. When the applet starts up you will see an animated schematic of a simple LRC circuit. The green color indicates positive voltage. The gray color indicates ground. A red color indicates negative voltage. The moving yellow dots indicate current.