Naming your city, much like naming your character in a role-playing game, can be as tedious and time-consuming as designing the city (or character) itself. And it'll be one of the first things you have to do when you get started with SimCity.
While you can always go for names you've picked up from other games, including Skyrim (Whiterun, Winterhold, Windhelm, etc.) or Fallout 3 (Rivet City, Paradise Falls, Grayditch, etc.) you might be more inclined to give your city a more generic sort of name.
To that end, there's the City & Town Name Generator from Mithrilandmages.com which pulls names from a database, culled from cities and towns across the United States and elsewhere, should you prefer something much more exotic.
The same site also hosts name generators for streets, medieval places, and terrain, should you choose to give names to landmarks in your city.
If you should find yourself stumped and unable to come up with a decent name for your city, just head on over to the site and find some inspiration.
SimCity is out on March 5 for the PC.