Up until now there's basically been only one game in town for small sites looking to earn money from publishing content-based ads. The virtual monopoly in this space has been the truly abysmal Adsense program from Google. (see earlier posts in this category)
Now Yahoo is finally entering the space as well.
Application link at http://publisher.yahoo.com/ Note that the program is still in the beta phase.
The more competition there is the better it will be for the rest of us.
So support Yahoo and the various small-fry out there such as adbrite, fastclick, tribalfusion, etc.