If you're thinking about taking a little trip to cap off the summer, check out Farecast-- they just opened their beta to include New York and a bunch of other cities. The service predicts fares over the next few weeks, so you can time your purchase to minimize the expense. For instance, the graph above shows the NYC to LA fares for late October.

Honestly, though, you're probably better off just going to Coney Island or Jones Beach-- that way you avoid the strip-search, liquid/gel/makeup confiscation, and hassle of the airport entirely.