Eagle or Spice for electronics(free).
Google sckechUp for basic 3d modeling for mechanics(free).
SolidWorks Academic version(I paid $80 for mine). 3d modeling, dynamic simulation and stress calculations. This is the real deal.
Blender for modeling if you know how to use it, can also do any kind of simulation if you can program in python(a use of the game engine). And best of all it is free.