I have found that the domestic flights price out pretty much the same between the individual carrier's websites and the sites like Travelocity, Expedia, Orbitz, etc. On international flights the prices are a lot different. Last year I was looking for a flight to Rome with the relatively cheapest being found on the British Air website when compared to other carrier's websites. Then I went to Travelocity and found the same seat on the same British Air flight at $200 cheaper than British Air's own site.