12. A computer program product, encoded on a computer-readable medium, operable to cause data processing apparatus to perform operations comprising: identifying, by one or more processors, a set of popular product queries, including: determining a number of occurrences of a first product model number of a first product in a plurality of prior queries of documents submitted by various users; verifying that the number of occurrences meets a specified threshold number of occurrences; and storing the first product model number in a database of popular product queries with model numbers of other products; identifying previous queries that were previously submitted by other users and specified the first product; identifying, within the previous queries that were previously submitted by the other users, attributes of the first product that were also specified in the previous queries; determining, for the first product, a product category that includes products having the attributes of the first product that were specified in the previous queries submitted by the other users, including accessing a database that lists product categories and corresponding attributes to identify the product category using the attributes of the first product that were specified in the previous queries; rendering, by the one or more processors in a graphical user interface, a search field configured to receive a search query; receiving, via the search field from a given user, a given query that specifies a first brand of the first product; selecting, as a query term for the given query, the first product model number from the set of popular product queries based on the first brand being specified by the given query; selecting, in response to receipt of the given query, a suggested product that has one or more same attributes as products in the determined product category and has a model number included in the set of popular product queries, wherein the suggested product is different than the first product and has a model number that differs from the first product model number and a brand that differs from the first brand; and in response to the given query that specifies the first brand of the first product: rendering, within a first region of the graphical user interface a search result that visually identifies the suggested product; and rendering, by the one or more processors within the first region of the graphical user interface, one or more search results that visually identify the first product, wherein the one or more search results that visually identify the first product include at least a URL configured to present an associated document corresponding to the URL for viewing through the graphical user interface.
13. The computer program product of claim 12 in which the given query comprises one or more of a product brand and a product model.