I would go for cityname.com if its available or otherwise mycityname.com or ourcityname.com
I want to create a portal for my city as well...and i am facing the same problem as you
I like CityNameGuide.com, if available.
Submit Your Webmaster Related Sites to the NB Directory
I swear, by my life and my love of it, that I will never live for the sake of another man, nor ask another man to live for mine.
citynamehall.com maybe ?