Even though I've seen Frank Caliendo do his John Madden impression roughly 36,000 times, it still makes me laugh. I'm like that four-year-old who just learned how to make farting noises.
Here's seven minutes of goodness from Caliendo's pre-Super Bowl appearance on Letterman. To be fair, he's done a great job of adjusting the impersonation over the years. The addition of Madden' frequent spaced-out silences is a nice touch.
Clip seen on the attention-whoring-but-not-all-that-bad Flash Sports Tonight (link has sound).