I thought I might add my 2 cents to this thread:
One London Place has to be my favourite building in the Forest City for sure!

It's an impressive symbol for London, and has such a beautiful design. Every angle I see it, it appears different with it's triangular shape. It even manages to seem very tall every time I'm around it. Definately it's the nicest building in SW Ontario, and perhaps all of Ontario outside the GTA (Hamilton, Windsor, and KW got nothing on it). Thank god we have it to take away from all the less than desirable looking buildings in our Downtown.
Anyways, some of my other favourites would have to be the Dominion Public Building since it's our oldest "skyscraper", and the former courthouse. Also the new market is quite nice with its public square. The TD towers are alright and they scream big city to me (they look really imposing when you drive down Hamilton). The Royal Bank Tower, the Talbot Centre and the massive London Life building bring their own charm to the city as well.