Okay, I know we've recently had a "Best D&D product ever" thread. This isn't quite the same thing.
If you'd be so kind, please list:
1) Your favorite OD&D supplement (such as they were)
2) Your favorite Basic D&D supplement (and ID which Basic set it was for, if you know)
3) Your favorite 1E AD&D supplement
4) Your favorite 2E AD&D supplement
Core rulebooks are not elligible. If you didn't play a given edition, feel free to ignore that entry.
Note that this doesn't have to be "the best" supplement. Don't worry about whether it accomplished a specific goal, or was well put together. I want to know your favorite--the one you got the most game use out of, or enjoyed reading/playing the most, or what have you. I'd also love to know why it was your favorite, if you're so inclined.
Thanks.