Also note that many cities have options for which "directions" you seek - automobile, walking, transit or bicycle. When you select "bicycle" the map will add a layer of green to indicate routes that have been designated as "bicycle friendly". This is merely a starting point, though, because I've found that some of the streets highlighted in green are not ones I would choose to ride on.

Another mapping utility is "mapmyride" www.mapmyride.com which also has an iPhone/Droid app that can do a GPS-based mapping function.