USA Cities Website Links

Chicago

Chicago Mayor's Office of Special Events The official Chicago events website, including information about the annual Air and Water show, an airshow which takes place along the Lake Michigan waterfront.

New York

New York Visitor's Bureau The official New York City marketing and tourism organization website used to be at nycvisit.com, but they've moved it to nycgo.com for some unfathomable reason.   The website seems to be geared towards selling stuff to visitors, but there is a small amount of useful information on the attractions page.   Last visited in April of 2009.
NYC.gov The official New York City website has links to pretty much anything you can think of in the city.
New York subway The official website of the New York subway system, which is the most practical way for most people, tourists included, to get around the city.
Metropolitan Museum of Art The official website of the Metropolitan Museum of Art, which includes a virtual collection of some of the pieces of art from ancient and modern cultures around the world, including Egyptian, Maya, Pacific and many others.
New York Aquarium The New York aquarium has tanks of fish like sharks and stingrays, and outside tanks and enclosures for beluga whales, walruses (which like to squirt their keepers with water) and performing dolphins.
Brooklyn Art Museum The Brooklyn Art Museum fought constant running battles against New York mayor Rudolph Guiliani, who got upset by exhibits such as a Madonna made of elephant excrement.
Brooklyn botanical garden I never got a chance to visit the Brooklyn botanical garden, but the website looks good.

San Diego

San Diego Zoo The official website of the San Diego zoo.
Sea World The official website of Sea World.