North America:
San Francisco, New York, Quebec City

South America:
Buenos Aires, Rio de Janiero, Asuncion (used to live there so I'm biased)

Europe:
London, Paris, Lisbon

Asia:
Siem Reap, Beijing, Tokoyo

Australasia:
Aukland, Perth....(only two I really like)

Middle East:
Jeruselem, Damascus....(only two I know)