The Gator Hardshells mentioned above are a lightweight, long wearing tire, but potentially a bit slick. Perhaps a summer tire.
The toughest, and best traction tire I've found so far is the Michelin Protek Cross Max. I found it had good traction, even in light slush.
Unfortunately a little bit slow of a tire, and not my favorite "century" tire, but it would make a good City tire.