The problem is that airfares are going up everywhere. Fares are likely to be higher next year than last.
I fully agree with Swampeast Mike that Turkish Airlines is a great airline. They are certainly not cheap, but the service is excellent—you get a lot for your money.
As for airfares from North America, late March is when they seem to begin their rise (eastbound, to Turkey). Mid- to late summer is when they're highest westbound.
Numerous tools can help you choose the lowest fare. American Express's "FareWatcher" utility is one such: it follows fares to your chosen destinations and sends alerts via email. There are others. Here's more:http://www.turkeytravelplanner.com/trans/Air/index.html