You can take the Piccadilly Line straight from Heathrow to the centre of town. The Heathrow Express is quicker, running direct from the airport to Paddington, but costs more. A taxi is really expensive, and not always quicker. There's also an Express running direct from the Gatwick Airport to Victoria, though other trains run the route. The Stansted Express runs every 15 minutes from Stansted Airport and reaches Liverpool Street Station in 45 minutes. Alternatively you can get off at Tottenham Hale and take the Victoria Line into town.
Getting around London can be a pain the neck at times as the underground isn't always the most reliable and can get very busy. The Circle and District Lines should be avoided if possible, and often the bus is the better, less stressful option. The Tube website isn't especially helpful for planning a route with the underground, but has a pretty good tool for finding and planning bus routes. The best option for traveling in London is to buy an oyster card, which can be used for both the tube and buses.
London now offers a city-wide cycle hire scheme. Boris, the Mayor, introduced it recently. Using your credit card, it's pretty easy to hire a bike from an automated station, ride around and then drop it off at another station somewhere else in town. Unfortunately there's the small matter of how easy it is to get around on a bike in London. Our guests coming from The Netherlands wont find it quite so bike friendly as they might be used to. If the Gods do smile on you and you happen to find one of the few roads with a bike lane, the chances are a parked car will by blocking the way.
