You may not be familiar with airfarewatchdog.com and you might want to check it out. It seems they collect the best prices from every city on a single page and the best prices to every city also on another single page. For example, on this page they list all the best current prices they’ve found going to London, including multiple deals for cities where prices go up or down depending on the season.

Right now they show the best prices going to London from these cities current as:

• Los Angeles – $786
• New York City – $614
• Montreal – $809

Many of the deals they show start for flights beginning in early September, which makes sense and is valuable information for anyone trying to best time their trip to when the good fares are available.