Free online circuit simulator
Doing a quick search on EE.SE I found: Free circuit simulator for educational purposes

Falstad seems to support animated electrons, and it is free.

However, if you are willing to shell out 10 bucks, I highly recommend EveryCircuit. It supports


Adjusting component values mid-simulation and seeing the effects in real-time.
A large variety of components.
Intuitive, and smooth animation: i.e. the electrons move faster for large currents/small currents, LEDs have varying brightness.


Here's a screenshot of EveryCircuit:



There is a free app version and an online version also.