Kizyr wrote:- London: gates in front of Buckingham Palace
This would be very hard to do successfully. Not only are the gates quite long, but there's always a massive dense crowd there and, if there's an event or the changing of the guard that's only going to be worse.
I wouldn't go with St Paul's cathedral, again, due to crowds of tourists, or any of the bridges due to the size of the area you'd be trying to meet in.
I believe the "standard" one is by the base of Nelson's column, but that also suffers from being a reasonable area and, if there's an event, enormous crowds.
The statue of Eros in Picadilly circus would be a better meeting point, the busy-ness isn't too bad and it's a very small area.