Most digital displays are completely solid state, with no moving parts. But check out these nifty (and noisy) Alfa Zeta 7-segment displays from FlipDots, which look digital, but use magnetic fields to change states. Check out more cool FlipDot demonstrations here and here.
Make: author Caleb Kraft came across this nifty plaything by Mike’s Electric Stuff, which uses sensors and a cylindrical grid of LEDs that simulate falling snow or sand as it’s flipped end-over-end. Mike needs to turn this thing into a toy you can buy. He’d sell thousands.
One of the more entertaining robotic groups we’ve heard was built by FT Mechatronics, whose electronic band consists of a variety of stepper motors, solenoids, hard drives, oscilloscopes, a robot xylophone, nixie tubes, and a tesla coil. Here, it plays Hello by OMFG.