yumchaa (Soho)
Given that this is a tea place, I have always had tea here. Incidentally I always seem to come here when it's warm, so it's always iced teas for me.
Nice place for people watching, thanks to its huge windows.
It also looks like a good place to work from, as I think there is wi-fi (and there's always a few people with laptops), but I haven't tried it myself.