While you can probably meet someone worthwhile almost anywhere, there are some places that make it a much tougher prospect. For instance, a comic book convention is probably not the best place to meet a non-nerd (though an attractive woman who sort of digs Battlestar Gallactica would be a queen there). A friend mentioned recently that going to the grocery store and dropping fruit is actually a good way to meet a dude. (My new buddy LostPlum tries it out on her blog, check it.)
Here are a handful of absolute gems for meeting someone new. (Note: sarcasm doesn't come across well in writing—assume that one or more of these are just jokes. Also, some of these places are good for men, others for women.)
A minor league women's soccer match. Sure, most men hate women's sport, but there will likely be plenty of women there who like sports. And, for a guy, the only competition is from male refs… men who'd rather tell people they're doing something wrong than actually compete (or appreciate the sport for its grace, beauty and ferocity).
A wine tasting. Weird, I think alcohol is a great idea—but a wine tasting is not a bar crawl. It's classy (sometimes) and allows you to talk about oaky aftertastes and only partly sound like a dingus. Plus everyone seems to have really tolerated that movie Sideways. Any sort of food / beverage thing would probably do, though social lubricant is helpful.
A language class. (Yes, this was covered in Fun & Free a few weeks ago, it's still a good idea.) If you both want to learn the same language, you may have a lot more in common. Maybe you could journey to a country in which you could sprechen zat language together? Hmm?
A karate class. Nothing gets the old ticker a-tickin' like a bit of exercise and a touch of violence. Plus you'll probably get a very close approximation of his / her "O face" when they're breaking boards (with their bare hands, bro).
Skydiving. While it might be a bad idea to try to chat someone up while you're both hurtling toward the earth, meeting them on the ground works. Then again, there's supposed to be some species of raptor that copulates while falling. Just sayin'. C'mon, you're daredevils, right?
An actual meat market. Sorry, it's a fact: people who like steak like people who like steak. Also, you don't make friends with salad.
Book signing. Already you have an item of mutual interest—that author—now just seal the deal. This can probably be exchanged for movie screenings or gallery openings. Keep in mind that you don't have to show off how much you know about the subject. You really don't.