Simulating Arduino circuits?

[dentaku]

Proteus/Isis has an Arduino emulator (hardly beginner stuff)
VBB Virtual Breadboard has an Arduino simulator and it looks nice but it's not free (still very reasonable priced).
Virtronics - Simulator for Arduino could possibly be useful but limited and seems to be unstable.

Question: Is there anything else out there that is good for simulating Arduino circuits?

[dannyf]

Anything that can simulate an AVR can simulate Arduino.