If this is your first trip to London then I wouldnt fool around with trying to get out to STN
- knowing London and the crappy transport system the train out from Liverpool Street station will be broken down and youll have to take a bus and it could get right nasty. And actually, when you add on the cost of the return ticket on the train then flights on Ryanair or any of the others going out of there are actually more expensive than taking the mainliners out of LHR
If you look at ba.com, make sure you click on the country of residence as UK so you can get the right fares and see when the priciest ones are. i would also recommend traveljungle.us (click on the uk flag) itll search all the low cost and normal airlines for you for the cheapest flights. ALso, British Midland, check their site- remember you get miles on VS
flights (not many, but 500 is better than none) and those flights are most likely to shoehorn nicely with a VS
One more thing, just keep in mind that flying in from another destination on the day you are supposed to leave can end up in one very long and tiring day-therefore keep it simple and keep away from airport interchanges and too long intra Europe flight. I guess from your nick that you are probably only going to the NYC area and thats a much shorter flight than mine out here to the West Coast, but as someone who has gone CPH
in one day, its not something i advise!