Google Maps has upped its considerable offering to include "Street View," which offers views of the certain locations at the street-level imagery. The areas where you can see images are noted by blue lines on the map (click the "Street View" button). Manhattan is pretty covered and downtown Brooklyn is covered, but the Bronx, Queens and State Island views are pretty much limited by major roads. Below is 1 Centre Street; you can't get an image of City Hall, because the blue line doesn't go into City Hall Park. Here's what Eastern Parkway at the Brooklyn Library looks like and this is the Verrazano-Narrows Bridge.
In the meantime, Microsoft's Live Search Maps has launched "photo-realistic, 3D imagery" of New York City. This is what their press release says:
Have you always wanted to visit New York City, but never had the chance to make it happen? Have you lived in the city for years, but still struggle to find your way around? Microsoft Corp. is making it easy to find the city landmarks, people and businesses that are important to you — giving you a sense of what it’s like to really be there — with the launch of New York City in 3-D.
There will be real-time traffic information and listings included. Here's the view from Central Park, looking south (and here's a higher-res picture).
They both pretty cool: Google is giving a view that most people see while Microsoft offers a view "few people — apart from Superman — have ever seen." Which reminds us - we're going to inspect our neighbor's roof deck.