Wellington, New Zealand. Small and compact, though lots to do. Tons of nightlife. Very walkable city built on a harbour with hills surrounding it affording many great views of the City below.
I also really enjoyed my time in Oslo. I wouldn't put it as a "great" city, but I found it to be a very decent city with lots to do and see and easy to get around. There are a lot of parks that were heavily used when I was there that I felt like sitting down and watch the people go about their way.
Others worth mentioning: London, NY, Boston, Chicago, Stockholm, Santiagp, Chile, Madison, Wisconsin and Vancouver.