Bike Pittsburgh has posted some great, sortable data about how commuters get to work in major American cities, drawn from a Census Bureau report. As you'd expect, New York comes in as the city where the least amount of people commute solo by car -- only 23.3 percent, followed by 37.2 percent in Washington, D.C. and 38.4 percent in San Francisco. Wichita, Kansas ranks as the place with the highest percentage of drivers: 85.1 percent of commuters use a car to get to work. The unfortunate national median for commuting by car is 74.15 percent.
There's also an interesting chart on bike commuting trends by gender, in response to a Scientific American article which posits that cycling needs to be made more attractive to women in order to boost overall urban cycling numbers. The argument seems to check out: according to Bike Pittsburgh's data, even in cities with relatively high levels of bike commuters, men cycle to work significantly more than women.