www.lastminutetravel.com aspires to do this. It's not working properly today, but in the past I have been able to specify DFW to ANYWHERE. You can do the opposite as well. They have it set up to sort by airline, price, destination, etc.

It seems that the airline list was much more extensive before. So I'm wondering whether the site provides it as a service hoping you will book through them, or if each airline or tour agency pays them ... or if the site just isn't working today.