No visit to New York City would be complete without a visit to the observation deck at the Empire State Building. You can see seemingly forever on clear days, and discern all of New York's landmarks. The admission fee is steep, but worth it. However, don't bother going up on days when the top is in the clouds. The view is the whole show, but when it's on, boy is it on!
Tip: Best times to go to avoid the crowds are early in the morning and late in the evening. The sunsets can be spectacular, but after dark is when it gets really romantic.