I found this rather slick circuit simulator the other day. It visualizes voltage (line color), current (speed of dots) and power (color of elements) through a circuit. Input and output voltages are drawn real-time as well. Comes with a bunch of basic circuits, from Ohm's law, voltage dividers, capacitors, RLC circuits, diodes, BJT, MOSFETs, logic, filters, etc. Well worth a look!

Excellent find!