Whether you live in the city or are just visiting as a tourist, the Transport for London (TFL) website is your new best friend. This website makes it simple to navigate all of the public transportation systems in the greater London area.
The maps on the website include options for walking, the tube, buses, the DLR, transport on the river, trams, rail and cycling. All you need to do is enter your departure area, which can be a stop or station, post code, street address or point of interest and your destination. The Transport for London website will determine the best way for you to get your destination with simple instructions on where to change mode of transportation. Best of all, the website integrates any delays or problems with the mode of transports and will reroute you if necessary.
The site also allows you to purchase and top up Oyster cards, which are the rechargeable cards used to access public transportation including the Tube, buses and some trains. Using the Oyster card does give you a discount on the fares for most transport systems in the city. You need to pay a small deposit to get a new card, but this is refunded if you return the card after your use, which makes it a great option for tourists and relieves the nuisance of needing to constantly wait in line at the ticket machines in busier tube stations.
Journey Planner: http://www.tfl.gov.uk