Rollyo is based on Yahoo Search. You select up to 25 sites that you would like to search, then you can place a search box on your site that will search only these sites. Rollyo also offers a variety of tools for sharing these searchrolls with others and for saving a list of searchrolls created by others that you like and want to use again.
Eurekster Swicki is also based on Yahoo Search. You can't limit it to certain sites, but you can (and are encouraged to) filter it to certain topics. You can also set certain sites to appear as featured results. The selling point is that users can rank the search results and those with a lot of votes will rise to the top while poor search results can be removed. It is thus interactive with the community of users.
Later: Apparently based on Eurekster Swicki is PreFound, which allows users to submit useful serach results they found on various topics, then there is an Swicki so that people can rate the search results.