Coming from Europe there are lots of options, including flying, train, bus and driving.
Train: If you live near Brussels, Paris or Lille we would strongly recommend the Eurostar train service as the best way to get to London. Trains to Paris take around 2hours 20mins, and for adults cost between €65 (non-flexible economy if you book well ahead) to €165 (flexible economy) and €250 (fully flexible business). Although you still have to check-in for the trains (make sure you follow the latest check-in instructions on your ticket, especially at Lille where check-in is surprisingly slow) the whole experience is much more pleasant than struggling around airports, and you end up right in the centre of London, at St Pancras, next to Kings Cross.
Flying: for information please click on the flights and airports tab.
Driving: Although you can drive from the continent via the Eurotunnel terminal at Calais in France, we do not recommend actually driving into London. Parking is extremely expensive (and in addition you will have to pay for the congestion charge in the center of London) and the traffic horrendous. Return trips through the tunnel with Eurotunnel cost around 170€ to 400€ depending upon the type of ticket and when you leave; you don't have to book ahead, but it is strongly advisable. The actual trip through the tunnel takes about 30minutes, but queuing and getting loaded onto the trains that carry your car takes another 30mins-1hour depending how busy they are. The drive from Dover to Central London takes about 1h 40mins, outside of rush hour.
Bus: Getting to London by bus is usually a cheap, but very time-consuming method. For example from Amsterdam to London (one of the most popular routes) it is about 11hours. Most of the coaches arrive at Victoria coach station: Eurolines and National Express.