3-D Electrostatic Fields 1.3c
Demonstrates electric fields in various 3-D situations
You can select from a number of fields and see how particles move in the field if it is treated as either a velocity field (where the particles move along the field lines) or an actual force field (where the particles move as if they were charged particles). This helps you visualize the field.
The menu in the upper right has a variety of different fields to choose from.