Sandpile applet by Bryan Head and David Perkinson (Highly recommended!)
Sage sandpiles might also come in useful.
This page has a file of MAGMA code attached (see files section at bottom). Ask Ben if you need a tutorial.
Floyd's cycle detection algorithm allows you to check when a parallel chip-firing or rotor-routing configuration has reached a periodic state without storing all the past states.
Here is code for automating chip firing steps on the ladder graph. Once you run it, you can type in the numbers of chips (separated by spaces, and one "enter" from top to bottom) and then each time you hit enter after that, it will advance one step.
For instance, if you run it then type:
5 5 5 5 5
0 0 0 0 0
hitting enter one more time should give
4 4 4 4 4
1 1 1 1 1
etc. Let me (Josh) know if you have any problems.
I also made a "fancy" point-and-click rotor-routing applet you can find here. Click to make a new vertex, click on two vertices to connect them with an edge, and click the box in the top left to advance a step (it currently only does rotor routing with two chips, both of which start at the first vertex you place).