One site that I have just examined is:
www.compete4yourseat.com
It allows you to post an itinerary on the site, then travel agents can bid on it. You are not obligated to accept.
I tried a trial run, and chose an itintery from SJ to Indpls leaving on a monday and returning on a Monday. I received a bid of $559. When I checked the identical itinerary on Continental, it was $720.00.
It seems that the travel agents have a way of staying in the business. The report said it works better for booking an immediate advance.
I followed two itineraries for flights through June. It seems that the best prices were further out. They jacked the Continental flight up to over $700 a few days before the flight. The jet was only 2/3 full.
The price of oil seems to be jacking the price up. I've seen the price fall from above $600 to now below $600 as the price of oil falls.