Truveo -- specialized, programmable video search

The first search engines simply looked for key terms in Web pages. Searches quickly became "smarter" -- giving more weight if a term was used in a first line or heading, looking at the proximity of search terms, etc. (These techniques were developed and tested by people like H. P. Luhn in the late 1950s). Google rose to prominence by using the number of links to a page as a measure of its popularity and hence relevance. Search engines are becoming ever more sophisticated.

We are also seeing the rise of specialized search engines. A good example is Truveo. Truveo only searches for video clips, but it is comprehensive with searches of given categories, channels (like CNN or ESPN), tags, etc. Perhaps more important, the application programming interface allows developers to incorporate Truveo searches into their Web sites.

Can you find other, specialized search engines? If so, do they have application programming interfaces that allow them to be used by others?