My current favourite though is James Blunt's "You're Beautiful". "What?" you're saying, "She's finally gone mad, that's not about the tube". Well it may not specifically be about the London Underground, (although he's a Brit so why not?) but it's certainly about passing someone on a crowded subway and sharing a bit of a "moment" with them, thinking "They're beautiful" or "They're hot" and realising that you will never see them again (unless I saw you today.com can come to the rescue). Not something that happens to me a lot, I'll admit, but doing that mutual double take with someone on the Tube has certainly has happened a few times. The full lyrics to "You're Beautiful" are here and you can watch the realplay video or windows video here.
Anyway, there's more song titles that might inspire you to think of your favourite on my main site and also Geoff has done a round up of London Underground and train related songs too. Have we missed any, and what's your favourite? Have fun!