A series of smaller Arduino projects using simple mechanisms, LEDs, button inputs, servo and DC motors, resistors, H-bridges, etc. culminated in a term project using spinning pinwheels to indicate which of a collaborating pair is dominating the conversation.
As a computer science undergraduate, I enrolled in an introductory electrical and computer engineering course and promptly watched my h-bridge go up in magic smoke during my first lab. This experience effectively scared me off from electrical components until I was in graduate school and enrolled in the Making Things Interactive course in which I learned that I was actually quite capable of using resistors, H-bridges, motors, and small computers. No magic smoke necessary!
Talk-o-matic. The Talk-O-Matic takes input from two separate microphones, compares the audio input with an Arduino, and moves the pinwheel gear motor associated with the more active microphone. If input is approximately equal, both pinwheels will move. The Talk-O-Matic also has an on/off button that resets the system.
Shadow Puppet (/Haunted Shirt). I had originally wanted to do something Halloween related, and so I got into light-activated "puppets" and a "haunted shirt." There were a couple possibilities for puppets, but I decided that a snake design with an accordion midsection would be simplest. This project has a snake puppet that slithers up and down via DC motors. It moves when the lights are on, and stops when they are off.