Special events are definitely the key. Conventions, sporting events, etc.. are always good, especially if they are arranged alongside a long weekend or traditional holiday.

For example, last July 4 weekend, the Atlanta Braves had a four game series against the New York Mets in New York. The Friday afternoon flights between ATL and NYC that weekend had not only the regular business travelers, but also the folks flying up for the games and the folks taking a long weekend in NYC.