I recently launched a website that enables you pay transit fares with bitcoin. This service is available for several US cities, and the list is growing as I find time to research more transit systems in other cities. http://bitfare.org
The site is pretty simple at the moment, but if people find this useful then I might be inclined to add more features. For example, if one particular fare card system proves to be popular, then I could try to build an automatic interface for that system.
As an introductory offer, we will round up to the nearest whole integer for the USD/BTC rate (right now that would be 6.0) and will fulfil small orders prior to receiving bitcoins.