Shop rates between all the major online ticketing groups. If you plan on doing consistent travel overseas, check into getting a membership to
www.bestfares.com. I use them almost exclusively for overseas travel. To put it in perspective, I've NEVER paid more than $550 for an overseas ticket in the past 8 years of travel to Europe and Central America, off-season or peak season..
This is going to change with a trip to UAE next month, though, but I'll be saving close to $1K on the ticket as compared to other agencies and airlines, so Bestfares is still the best place for overseas rates that I've found...