From Read/Write Web:

There are an abundance of new search engines (100+ at last count ) - each pioneering some innovation in search technology. Here is a list of the top 17 innovations that, in our opinion, will prove disruptive in the future. These innovations are classified into four types: Query Pre-processing; Information Sources; Algorithm Improvement; Results Visualization and Post-processing.

(Link from John Batelle's Searchblog.)