Abbott & Costello's famous "Who's on First?" skit.
This is a short clip from the 1945 movie "The Naughty Nineties", and according to Wikipedia this is known as the finest recorded version of the skit. Whether or not that's true, it's funnier than anything I've ever heard. I laughed myself into a cough the first time I watched this.
.mp4 format to you can put it on a Zune, iPod or the the like easily.