I always feel the lights of a city at night bring out a very different dimension in it's character. Also, if you can get light trails from the traffic added in this mix, it really becomes amazing.
Thoughts on how the balance between light and darkness can be used to make these better?
City photographs at Night
It really depends on the color temperature I guess, sodium lights (yellow/orange) go very well with blue hour (see color theory as to why), whitish light... not so much - I'd probably go B&W then. Here is an example for sodium lights.