h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

It'd be good to mention all the cross-platform interchanges. Knowing where those are can really speed up your progress around the Underground... it's hugely quicker, for example to go from Waterloo to King's Cross via the Bakerloo Line and Oxford Circus than via the Northern Line and Warren Street or Euston because of the distance involved with the Victoria / Northern interchange.

These are all I can think of...

For the Underground ones:
Finsbury Park - Piccadilly to Victoria
Highbury and Islington - GN Electrics to Victoria
Euston - Northern to Victoria
Oxford Circus - Bakerloo to Victoria
Baker Street - Bakerloo to Jubilee
Stockwell - Northern to Victoria

Overground, excluding places where two lines share the same platforms (District & Circle, Hammersmith & City, Metropolitan and Circle, Piccadilly and District etc):
Hammersmith - Piccadilly to District
Barons Court - Piccadilly to District
Mile End - Central to District
Edgware Road - District & Circle to Hammersmith & City
Finchley Road - Metropolitan to Jubilee
Wembley Park - Metropolitan to Jubilee

For a lot of these, there's also a 'wrong' choice you can make that will take you a lot more time:
Piccadilly to Victoria - King's Cross St Pancras or Green Park (use Finsbury Park)
Piccadilly to District - Earls Court, South Kensington or Gloucester Road (use Barons Court or Hammersmith before the Piccadilly Line goes underground)
Hammersmith & City to District or Circle - Paddington (Edgware Road is about a mile shorter)
Metropolitan to Jubliee - Baker Street (use Wembley Park or Finchley Road)
Victoria to Northern - Euston or Warren Street (use Stockwell, if you're going to or coming from South London)
District to Central - Monument / Bank (the link between the two stations is about six miles long, use Mile End)

I might even do a separate entry on them, if there are enough. What d'you think?

Are there any others I've forgotten?

Good idea - I've always wondered why they didn't just build all the stations like Highbury & Islington...

I can't think of any more off the top of my head - I'll let you know if I do.

Come to think of it, another 'wrong choice' is Jubilee to Bakerloo at Waterloo, if you can manage to use Baker Street instead. It's bloody *miles* on that travelator.

And the main line trains always stop on the platform furthest from the 'right' end of the subway to the Northern line...