eBay and Craig’s List have appropriated classified advertising from newspapers. Some believe that Edgeio and similar services that vacuum classified listings from blogs based on ad-specific tags will spell the end for eBay and Craig’s List. Google is taking a stab at classifieds—including the ability to pay for an item directly from the site—with Google Base.

Now, as if the field isn’t crowded enough, Microsoft is entering the fray with Windows Live Expo.

To compete in this field, you’d better offer something different and compelling. Expo (in beta, of course) is linking its free classified service to social networks. According to Expo’s product unit manager, Garry Wiseman (quoted in a ClickZ News item), “What sets Windows Live Expo apart is that people can set their own search parameters for goods and services. They can define their own marketplace universe.”

So many behaviors have to change, and change differently for each of the new classified models. The one that drives the most behavior change is the one that produces the best results. I still like the Edgeio model, where you control your ad on your own site. Of course, that requires you to have a site in the first place. It’ll be a while before the winning model emerges. One thing for sure, though; it’s not likely newspapers will be involved.