I got a pair of nice SRF-08 ultrasonic rangefinders for a robot project some time ago and decided to test them out with a PC first. I built a I2C adaptor for the parallel port and wrote some logging/graphing code to display the time-of-flight for the first eight echos returned.
Nothing fancy, but it was interesting to see how different obstacles affected the readings, and I added a little ‘Theremin’ mode for fun, where the first echo determines the frequency of a tone.