One interesting service that I learned about today was a site search service called Collarity. They offer a site based search service that can display community-clustered search results based on previous users actions. The service can also deliver optimized ads with the search results allowing publishers another way to monetize content.
An example of an implementation can be found at the My Fox LA site. I think there are multiple stories to tell about this service, both from a user perspective and the site monetization angle. The results are different enough that I think it may take users some getting used to, but it certainly invokes interest as an alternative to the ineffective site search that exists on most web sites.