CityTownInfo.com and Expert Ratings provide alphabetical lists of cities in the United States. Wikipedia is additional resource that features an alphabetical list of international capital cities.
In addition to an alphabetical list of U.S. cities, CityTownInfo.com provides pertinent information on each city, such as population and the number of colleges in each city or town. Information on the population of each state is also available. Expert Rating offers a list of cities by state as well as by alphabetical order. The list of international capital cities on Wikipedia features pictures of flags for each country, territory or dependency. Additional information is available for some of the countries on the Wikipedia list.