I have checked most of the internet travel sites and to me it seems that the lowest rates are on Travelocity. Once I find what I want I then check the Hotel or Airline directly to check the rate. I then book with whoever has the best rate and terms.

You also have to be careful with the superdiscount sites since they may charge huge cancellation fees. I almost booked thru one of them for a convention stay until they told me the cancellation charges. Minimum of one nite in fees and it went up from there.