PhET simulation in town, and it caught my attention.
Actually, there are several new PhET sims available, and I've only had a chance to develop an activity for one of them so far.
The sim is Capacitor Lab, described by the PhET team as follows:
Explore how a capacitor works! Change the size of the plates and add a dielectric to see how it affects capacitance. Change the voltage and see charges built up on the plates. Shows the electric field in the capacitor. Measure voltage and electric field.
I wrote a quick activity, "'Lectronic Plates," that guides a bit of inquiry involving the uniform electric field between parallel plates. Charge density is introduced and explored, too. It only scratches the surface of this sim's potential (!), but it's a start.
I included a link on my Conceptual Physics Lab Manual PhET page, too. I hope to write a more extensive capacitor lesson soon. I'll post it when it's fairly stable.