CabEasy.com allows taxi travellers to share cab rides. Those looking to share a taxi can create new cab rides on a Google Map or browse the map to find the ones that match their route. They can then contact a fellow traveller and arrange to meet.
The service is very similar to the many car-pooling mash-ups built using the Google Maps API, only aimed at those who wish to share cabs rather than their own cars.
Drijo - auction off available seats in your car or search for free seats in other people's cars.
eMotorPool.com - Google Maps carpool search
Carpool - Google carpooling Mapplet
RoadSharing - car-pooling service that provides an easy way to find someone to share a trip with.
Cab4Me - Mobile service that shows your current location on a Google Map and attempts to find your nearest taxi provider.