The Strand - 8 miles of used books. 'Nuff said.
Forbidden Planet - comic shop across from The Strand.
Bluestockings - Radical bookstore and activist center. Specializing in gender, feminist and queer studies.
St. Mark's Bookshop - independent book store, opened until midnight.
Midtown Comics - on the second and third floors. Super selection.
Jim Hanley's Universe - a quite large comic book store near the Empire State building. Open until 11pm.
Partners & Crime - independent bookstore specializing in mysteries. Also a neat area to walk around.
Revolution Books - where revolutionaries go when they want a book.
Housing Works Bookstore Cafe - all merchandise is donated and 100% of the profits go to Housing Works, Inc.
Hue-Man Bookstore & Cafe - The area's largest selection of African-American literature and books.
Kitchen Arts & Letters - The ultimate foodie bookstore.
Unoppressive Non-Imperialist Bargain Books - self explanatory.
Hopstop - an excellent resource to plan how to get from point A to point B using public transportation.
NYC Wireless - hot spot map of free public wireless access. You can also get free access at any public library.
James A. Farley Post Office 421 Eighth Ave between 31st and 33rd Sts (24hr information 800-275-8777, usps.com). Open 24hrs (counter service: Mon-Fri 7am–10pm; Sat 9am–9pm; Sun 11am–7pm). This is the city’s main post office. Outside of counter-service hours, you can buy stamps and mail packages using automated self-service machines.
Vampire Freaks - goth, steampunk, cosplay clothes
Gothic Renaissance - goth, steampunk, cosplay clothes
Enchantments - witchcraft and goddess supply store.
Eataly - Mario Batali/Lidia Bastianich Italian food emporium
Century 21 Department Store - a giant discount department store.
Pearl River Mart - a two-story Chinese department store with lots of nifty stuff.
There's also fun shopping to be had along St. Mark's Place, Bleeker Street, Union Square, Herald Square, and, of course, 5th Avenue around 57th St.
If you are interested in seeing a show, you can head over to the Theater Development Fund's TKTS booth at Times Square for discounted day-of-performance tickets to many Broadway & Off-Broadway shows.
Empire State Building - 350 5th Ave (btw 33rd & 34th St). it's opened 8am-2am.
Saint Patrick's Cathedral
American Museum of Natural History
Central Park Zoo
Grand Central terminal
Metropolitan Museum of Art
Museum of Sex
New York Public Library
If I think of anything else, I'll add it to the end of this post. If you have any questions, post a comment and I'll do my best to answer them.