21. A memory device to store instructions that are executable by a processor of a network device, the instructions comprising: one or more instructions to receive, independent of any search query and from a first user, a selection of one or more documents, where the one or more documents are used to form a plurality of custom content groups; one or more instructions to index the one or more documents to form a custom search index for each of the plurality of custom content groups, where each custom search index is different from a web search index and any other custom search index associated with the plurality of content groups; one or more instructions to receive, from a second, different user, a selection of one or more of the plurality of custom content groups; one or more instructions to receive, from a client device associated with the second user, a search query; one or more instructions to perform, based on the search query, a search of the web search index to identify web search results; one or more instructions to perform, based on the search query, a search of one or more of the custom search indexes associated with the selected one or more custom content groups to identify custom search results; one or more instructions to generate a search result document that includes the web search results, the custom search results, and a plurality of advertisements presented within at least a first area and a second area of the search result document, where the first area is distinct from the second area within the search result document, where the web search results and one or more of the custom search results are included within the first area, and where the advertisements and another one or more of the custom search results are included within the second area; and one or more instructions to provide, to the client device, the search result document.
21. A memory device to store instructions that are executable by a processor of a network device, the instructions comprising: one or more instructions to receive, independent of any search query and from a first user, a selection of one or more documents, where the one or more documents are used to form a plurality of custom content groups; one or more instructions to index the one or more documents to form a custom search index for each of the plurality of custom content groups, where each custom search index is different from a web search index and any other custom search index associated with the plurality of content groups; one or more instructions to receive, from a second, different user, a selection of one or more of the plurality of custom content groups; one or more instructions to receive, from a client device associated with the second user, a search query; one or more instructions to perform, based on the search query, a search of the web search index to identify web search results; one or more instructions to perform, based on the search query, a search of one or more of the custom search indexes associated with the selected one or more custom content groups to identify custom search results; one or more instructions to generate a search result document that includes the web search results, the custom search results, and a plurality of advertisements presented within at least a first area and a second area of the search result document, where the first area is distinct from the second area within the search result document, where the web search results and one or more of the custom search results are included within the first area, and where the advertisements and another one or more of the custom search results are included within the second area; and one or more instructions to provide, to the client device, the search result document. 24. The device of claim 21 , where the one or more instructions to receive the selection of the one or more custom content groups further include: one or more instructions to provide the second user with a user interface, and one or more instructions to receive, from the second user and via the user interface, an identifier that identifies the one or more custom content groups.