This new wave of quizzes might be the king daddy of the geography genre. They incorporate a Flash game into the Sporcle quiz, which allows them to amp up the number of answers exponentially.
This one is one of my favorites: A U.S. city coverage map.
Basically, there's 3,815 cities in the U.S. of more than 10,000 people. Your job is to get them all by naming a city within 25, 50, 75 or 100 miles of it (you pick the difficulty level before you start). So if you type in "Dallas," for example, you'll get most (but not necessarily all) of the big suburbs in the Metroplex.
Fair warning, though. The Expert level (you get credit for any city within 25 miles of the one you type) is damn near impossible. I got into the 3,200s on my first few tries and then those midwestern cities that are juuuust far enough apart started to kick my ass. I'm up to 3,400 or 3,500 now after looking up a few more.
http://www.sporcle.com/games/darinh/us-city-coverage--map-quiz-
There's also a similar quiz for Europe. And if you're a real glutton for pain, ones where you have to list the 500 largest U.S. cities (on their own, no credit for others in the area) and the 2,500 largest world cities.
http://www.sporcle.com/games/darinh/500-largest-us-cities--map-quiz-
http://www.sporcle.com/games/darinh/european-city-coverage--map-quiz-
http://www.sporcle.com/games/darinh/2500-largest-world-cities--map-quiz-