Today's WSJ posits that as summer ends airfares will fall to almost reasonable levels, although higher than last year. Partly because fall is convention season apparently so businesses will be buying full fare or business class tix and apparently subsidizing the folks in steerage.
A well-known site called Scott's Cheap Flights agrees and says forget about summer travel, look ahead. It has presented what it calls the Goldilocks formula for buying tickets (not too early, not too late, just right). They say for domestic flights, 1 to 3 months in advance is best; for international, 2 to 8 months. For peak travel they suggest adding a few weeks.
Since most of the cheapest fares have a 21 day advance purchase requirement, they say use that 3 week rule as the final deadline to book.
YMMV, of course.