St. John the Divine cathedral is a perfect tourist attraction during travel to New York City. It's inexpensive, easy to get to, and amazingly beautiful... and it's the largest church in all of North America!
St. Paul's Chapel - Trinity Church in Ground Zero. Survived 9/11 unscathed only 1 block away! Inside there's an incredibly impressive exposition of the chapel's function in the aftermath of 9/11. This church is also where George Washington's inauguration was held. I've been to NYC a couple times and still haven't managed to make it here.