An oldie but goodie -- Skycraper.org's five year old Transparent NYC map, which lets you overlay all sorts of information on a map of Manhattan Island. After you check that our, explore the Skyscraper site, which has a bunch of other cool NYC webprojects, and lots of information about the Skyscraper Museum in Battery Park City, which is one of many museums you can visit downtown. The current exhibit is the Top Ten Skyscrapers of New York, as picked by 100 experts.