17. A computer-readable memory device to store instructions executable by at least one processor to cause the at least one processor to: store search query-search document associations, each search query-search document association representing a one-to-one pairing of an issued search query and a search document retrieved based on the issued search query; receive a search query; identify a set of search result documents using the received search query; form a plurality of clusters of search documents, of the stored search query-search document associations, that are associated with the identified set of search result documents; select at least one of the plurality of clusters; compute a centroid for each of the selected at least one of the plurality of clusters: compute a score for each unique issued search query associated with a document in the selected at least one of a plurality of clusters based on the computed centroid; formulate a search query refinement suggestion based on the computed scores; and sort the formulated search query refinement suggestion among a group of search query refinement suggestions.
17. A computer-readable memory device to store instructions executable by at least one processor to cause the at least one processor to: store search query-search document associations, each search query-search document association representing a one-to-one pairing of an issued search query and a search document retrieved based on the issued search query; receive a search query; identify a set of search result documents using the received search query; form a plurality of clusters of search documents, of the stored search query-search document associations, that are associated with the identified set of search result documents; select at least one of the plurality of clusters; compute a centroid for each of the selected at least one of the plurality of clusters: compute a score for each unique issued search query associated with a document in the selected at least one of a plurality of clusters based on the computed centroid; formulate a search query refinement suggestion based on the computed scores; and sort the formulated search query refinement suggestion among a group of search query refinement suggestions. 18. The computer-readable memory device of claim 17 , further comprising one or more instructions to cause the at least one processor to: normalize the term vectors; and form clusters of the identified search documents based on distances of each of the normalized term vectors from a common origin identify search documents of the search query-search document associations that match the at least one of the search result documents; and use the issued search queries, associated with the issued search documents, in the formulating.