1. A computer-implemented method of determining search results related to a search query, the method comprising: receiving a search query from a computer via a computer network; submitting the search query to a plurality of search engines; receiving, from the plurality of search engines, at least one ranked list of search results based on the search query, the at least one ranked list of search results including a first ranked list of search results received from a first search engine of the plurality of search engines, wherein the first ranked list is without actual relevance values supplied by the first search engine; providing an estimated relevance value for each search result in the first ranked list by: determining an estimated relevance value for a most relevant search result of the first ranked list; determining an estimated relevance value for a less relevant search result of the first ranked list; and determining other estimated relevance values for the search results in the first ranked list based on the estimated relevance value for the most relevant search result and the estimated relevance value for the less relevant search result; determining, for each of the plurality of search engines, a weighting value; determining a weighted relevance value for each search result based on the estimated relevance value when an actual relevance value was not received for the search result from one of the plurality of search engines, the actual relevance value of the search result when the actual relevance value was received for the search result, and the weighting value associated with the search engine that provided the search result; combining the search results into a single list; sorting the search results in the single list based on the weighted relevance values; and sending at least a portion of the single list to the computer via the computer network for display to a user.