1.05 has made great strides on keyboard shortcuts.  The numpad key now works pretty well for unit movement, and TAB works well for selecting and then cycling through units.  Unless I'm mistaken, though, selecting and cycling through cities is somewhat more difficult.  Shift-C will select a city, but only if one is idle; otherwise I can't find a way to select a city with the keyboard if a unit or other non-city object is already selected.  Likewise, PgUp/PgDown do cycle through cities, but only if a city is already selected in the first place -- and it's not clear to me why PgUp selects some cities and PgDown selects others.  

Accordingly, I'd suggest a single key (preferably a letter key without an additional keypress of a shift or ctl or alt), such as the "Y" or "T" key, that would (1) select a city if one isn't already selected, and (2) cycle to next city if a city already is selected.  (Forgive me if this is already in!)