I am MechE (my school doesnt use ME to define mechanical engineering).
Mechanical engineers understand transfer of forces, controls, vibrations, fluids, and heat. They build everything from rocket engines, computer harddrives, cars, computer models of biology, circuit boards (the mechanical aspect), MEMS, piping, nuclear reactors, and in my case, ROBOTSSSSSSSSSS!!!
MechE can basically gaurantee a job in just about any field if you are good at it. They are in high demand, and get like $52k+ starting salary right out of college. Only ECE and CS can get you a higher salary, but are more limited in scope . . .