Stansted and Gatwick

From Gatwick, you take the Gatwick Express which costs 28 quid roundtrip, and takes about 30 minutes. Trains leave from Victoria Station (Zone 1--Victoria, Cirle & District Lines).

From Stansted, you take the Stansted Express, which takes about 45 minutes, costs about 30 pounds roundtrip, and drops you off at Liverpool Street Station (Central, Circle, Metropolitan, Hammersmith & City, and Overground Lines).

If you need to go to 'The City,' Liverpool Street is closer (JP Morgan, Merrill, Deutsche, UBS, RBS, Blackrock, The World Bank, most brokers). If you need to go to West London (almost all of the hedge funds, Lazard, Blackstone, Greenhill, Evercore, Bain Capital, Bernstein, McKinsey, BCG, GE Capital, all of the high-end stores, all of the best clubs and restaurants, almost all of the embassies), then go to Victoria and take the Victoria Line to Green Park..

If you're going to Goldman, Blackfriars is closest, but it's closed, so you should go to Chancery Lane (Central Line) and walk.

If you have to go out to Canary Wharf (MS, CS, HSBC, Citi, Barclays, BGI, State Street, KPMG, parts of BoA, a few brokers), take the Jubillee Line from Green Park, the DLR from Bank, or take a cab (it's about 20 quid from The City).