Back in the day, you needed some pretty serious gear to measure the speed of light:
[Fizeau] shone a light between the teeth of a rapidly rotating toothed wheel. A mirror reflected the beam back between the same gap between the teeth of the wheel.
There were over a hundred teeth in the wheel. The wheel rotated at hundreds of times a second — therefore thousandths of a second was easy to measure. Light was reflected from mirrors more than 5 miles apart. This also helped him making accurate measurements.
(That’s from what-is-the-speed-of-light.com, your one-stop shop for speed-of-light related inquiries.)
Nowadays it’s much easier: All you need is a microwave.
(Link via Boing Boing.)