Grand Central is big and beautiful and it also periodically hosts free cultural events - poets at typewriters custom-composing poems on demand - or Alvin Ailey dancers performing in Artist, Nick Cave's horse suits!
I love sneaking over here in the middle of the day to see a movie - they always have the best selection of films. I recently saw Pina in 3D and The Kid with a Bike here, and another time I saw Bela Fleck play the banjo after a screening of Throw Down Your Heart.
My favorite place on Bedford Avenue, this bookstore has both new and used titles. If you're patient and look close enough, you can usually find a book that's worth more than they're asking. Not to mention their stellar selection of magazine titles. Good for design, art, photography, sociology, fiction, and everything in between.