Wei-Hwa's Memory Lists Puzzle

As I've said before, Wei-Hwa Huang produces a puzzle gadget for your Google home page, in which new puzzles show up from time to time. The last one was more trivia-oriented than his normal fare, and might appeal to those of you who like that kind of thing. Given a category, name all the members of the set in a given time. Some examples are "Snow White's Seven Dwarves" or "The Fifty States." Of course there's also topics such as "the Mohs scale for hardness."