The website NYC Tourist has several detailed maps of Manhattan. It also provides maps of the surrounding areas of Manhattan, including all of New York.
One map available on NYC Tourist breaks Manhattan down into its various neighborhoods. These include major areas such as Times Square and Harlem as well as lesser-known neighborhoods such as Gramercy. For the more popular, tourist-heavy neighborhoods, there are additional maps that show major buildings and streets. Another map on the website shows the bus routes in Manhattan in great detail. Yet another map serves a similar purpose but shows the various subway lines throughout the city.