I've collected about 57,000 cities from a city field found in LJ user foaf feeds. This field has its problems. It might be blank 90% of the time, people write mumbo jumbo in it, and people often write the same city's name more than one way. Still, it can sense large city names.
These are the most common cities among actively-posting LJers's:
users | city
926 | Moscow
857 | Москва (Moscow)
346 | Seattle
205 | San+Francisco
202 | Toronto
200 | Chicago
197 | London
195 | Portland
159 | New+York
151 | Austin
145 | Los+Angeles
138 | Melbourne
135 | Санкт-Петербург (St. Petersburg)
128 | Boston
123 | Minneapolis
107 | Brooklyn
103 | Atlanta
103 | Vancouver