Every Jeopardy! Clue and Response, Ever*
Let's say you wanted to know what went down on last night's episode of Jeopardy! Well, you'd be in luck -- browse on over to the Show #6128 page on J! Archive, and there you have it -- every clue, every response, all the scores, the whole thing -- you can basically play Jeopardy! for yourself by reading the clues, then mousing over the dollar amount to see the response -- remember to phrase your response in the form of a question.
At first I thought the J! Archive included every game, ever, but several readers pointed out specific shows that were missing. Check out the Help page for more information on this volunteer project -- including the useful note that some clues are blank, because they were never revealed on the show. There's also a delightfully nerdy discussion of various Rules, Conjectures, and Strategies, including "Clavin's Rule," named for Cliff Clavin's fictional Jeopardy! appearance on Cheers.
So, my nerds, go check out Season 20 and Season 21 to relive Ken Jennings's legendary run, or try Season 2 (from 1984) in which the second episode ended with a three-way tie at $0. Why? Just look at that Final Jeopardy! clue and I'll think you'll see the problem. (Modern nerds may be familiar with that kind of clue because we've lived through a century transition, but in 1984, none of the contestants had.)
* UPDATE: After reading the comments (including several from Jeopardy! contestants), the archive isn't as complete as I thought. The good news is that apparently you can contribute to it; check the site's Help page for info on who the archivists are; there's also a Suggest Correction form that presumably could be used to submit new info (though I'd recommend talking to a human about what format they want before transcribing a game).