As a bazillion blogs have already stated, Amazon's got a new search out called A9.com.
The one thing that appears that might set this search engine apart is that it will also search over any of the indexed books in Amazon's collection. This could be very useful for people doing research or homework.
They've still got a few issues they've got to tweak. I think they need to figure out a better way to page through results. It seems like you should have seperate paging for each type of search (although I can see while in split mode where have one paging mechanism would work well.) I also noticed that the same URL pulled up different descriptions depending on how the search was done. That didn't make sense to me. Try searching for the phrase "dan switzer" both with and without quotation marks around it and you'll see what I mean.