I was reading up on Jeopardy! (been watching it regularly since I moved back to California) and I learned that for April Fool’s Day in 1997*, Alex Trebek hosted Wheel of Fortune, with Pat Sajak and Vanna White as contestants. I managed to find the whole episode on Dailymotion. It’s kind of funny to see Trebek awkwardly out of his element (he makes a big goof in the bonus round) and he also seems much younger than he does today, while Sajak and White generally look the same, although the footage is pretty grainy. Of note: Trebek says the last time he’d been on Wheel was “sixteen years ago” and at the end he jokes that he can’t wait to be back in another sixteen years. If they decide to do it again next year, 2013, his joke will have come true 
*Same date as the Comic strip switcheroo, thereby making it The Best April Fool’s Day