TaxiWiz helps you carry exact change
Right now TaxiWiz covers 8 cities, New York, Boston, Chicago, Las Vegas, Los Angeles, San Francisco, Toronto, and San Diego.
The are also mobile versions for each city, which basically means you get the same web site, but without the map image.
Of course, the site only gives you accurate cab fares if your driver's not trying to rip you off. Since most of these cities have regulations in place to standardize cab fares, that means you should make sure to get in an official, license cab. That guy on the street corner who drives people around in the back of his station wagon can charge you whatever he feels like.
[via Uneasy Silence]