Coys of Kensington
For me, one of the very best bits about London is Coys of Kensington. It is in Queens Gate Mews, and you would NEVER find it if you weren't looking. I've been making the pilgrimage for years now; I took a date there once, saying there were some wonderful cars to see. Her reaction was "Oh... they're OLD cars.... But new cars are better than old cars". I didn't see her much after that.
More pictures, on My Other Stuff. If I'm encouraged I might post pictures of the cars I've owned.