Wikiseek seems to be the hottest news of the day but honestly it is just a poor mashup of the Wikipedia database, a poor quality search engine, and some PPC adverts. Whilst Wikiseek has launched in a huge fanfare, and admittedly is still in beta, my personal opinion is that Wikipedia are taking the wrong direction.
Google have just launched the Google Co-op Custom Search service.
The initial feedback I have seen from many bloggers is “more of the same”.
Google Co-op is not the same as Google Adsense for Search in many ways, and the new service can be used / abused in ways that Adsense for Search could not.