I race RC cars, placed 5th at the nationals last year. I also fly model gliders, dynamic soaring, where we hold the world speed record for ALL model aircraft, with unpowered model sailplanes. The WR today is 499mph!
Both these are more obsessions than hobbies though.
Here's a couple vids. These are slower vids, because the fastest vids you can't really see anything. Crank up the sound! These gliders make crazy sounds as they rip the air.