Finding cheaper (not cheapest) flights is part of my concierge work.
After finding decent deals to Florida within framework i was given, I turned my attention to deals for Summer travel.
For non stop flights from New York area to London, best listed prices were with 'unknown carrier' option.
You have to be willing to roll the dice as you will find out airline you will fly on after you complete booking your trip.
One way to feel more comfortable about choosing 'unknown carrier' is to compare flight times with main carrier schedules and you should be able to guess what airline you will land.
I noticed that some of the 'super saver' fares are pretty vague as far as time of flights and whether it will be a non-stop or 1 stop flight. I would personally stay away from these 'foggy' ones.
While Bing Travel shows a graph of price trends in past 30 days and makes recommendations on whether to buy now or wait, Momondo travel search engine offers a graph of price trends for the month when you plan to travel.
The other concern myself or any other traveler might have is can I trust booking through sites like Explore Trip, Vayama, CheapOair and others.
In an additional search on Momondo for travel from New York to Barcelona, Explore Trip offered pretty good prices on Iberia (with a caveat, 2 stops) while prices quoted for GoTravel123 were higher once I got on their site.
One has to decide when a $200 difference on a RT ticket is worth the minor inconveniences.
Next best fares on that Newark-Barcelona route (with only 1 stop) were listed on Vayama.
It takes some work to stretch your travel dollars.
(* Photo of Barafina restaurant from London Travel Guide by Momondo)