Tottenham Court Road
If you are driving, Tottenham Court Road is within the area in which you will have to pay the Congestion Charge.
The shiny new shops on the western side towards the bottom end all used to be grotty little sex shops touting adult CD-ROMs and the like. (Perhaps the idea was you buy something to view them with in one of the electric shops on the other side of the road?) They were knocked down around 2000 as the area was smartened-up a little.