What is the best way to get from Heathrow airport to the Waterloo train station?
If you're packing light and can easily schlepp your own luggage, take the tube: Piccadilly line from LHR to Hammersmith, District line to Embankment, Northern line to Waterloo. The trip will take an hour. Fare: £4. For a zoomable tube map, go here.
Just want to put a warning in here; Try to always avoid riding the tube during the week between 4 - 5:30 pm. Its pure H*ll.