There is only one or two that provide xml feeds the rest only offers aff. links ... If you want to promote, then go with these two companies that provide the feeds as otherwise you will loose out on potential revenue...

Anyway, it is quite sad that some offer you for a $800 flight only $5-8 commission .... Specialize is niches and provide more services then only flight and hotel bookings... and you might have a chance to fight the big sites ....