iOS/Android: Making the booking of taxis less of a hassle is an obvious smartphone application. We've already seen goCatch enter this space, and myTaxi offers a similar set of features.
As well as letting you see and book myTaxi-registered taxis in your vicinity, you can also get an estimate of the fare to your destination and rate individual drivers. Unlike goCatch, the app is available on Android and iOS platforms. Right now, the European developers are concentrating their Australian driver registration efforts in Sydney, so you'll have a better chance of tracking taxis in that city.
myTaxi is a free download for iOS and Android devices. If you try it for taxi booking, tell us your thoughts in the comments.