Charing Cross through London Bridge is a good one for urban scenery as elevated near the Thames through the main bit of London. Waterloo approach is not as good, but similarly has some sights from it. DLR from about Mudchute to where it dives down into a tunnel to Bank is a relatively good one for getting good views of modern skyscrapers.
The Piccadilly around the Sudburys/Alperton is pretty 'scenic' with views over West London, sadly there's not a huge amount to look at unless you know the area well. "Oh look it's Wembley Stadium from a few miles away".
As for the Met: Chesham, rather than Amersham. The Amersham route/GCML is basically continuous urban area, whereas the Chesham branch squiggles back down the side of the Chess Valley with the development only on the less scenic uphill side (and even then it's well hidden when there is development).