21 January, 2008
Good ol' Wikipedia
A simple question, I thought. I have a London Travelcard, bought primarily for rail use, but I wanted to check its zonal validity on the buses, which I knew was different from the rail/tube/DLR arrangements. After several minutes of frustratingly unproductive googling, I came upon a Wikipedia page providing precisely the information I required.
Of course caution is required, but Wikipedia is definitely one of the Web's killer apps.