1. A system for providing similar items to a user of an electronic catalog, the system comprising: a similarity mining module configured to detect similarities between items in an electronic catalog and create one or more sets of similar items, each set of similar items corresponding to an item in the electronic catalog; an attribute mining module configured to analyze each set of similar items to detect common attribute values of the similar items and to create an item data set comprising sets of items sharing one or more attribute values; and a similarity explorer module comprising computer hardware, the similarity explorer module accessible by a user from an item detail display of a first item selected by the user, the similarity explorer module configured to: output a plurality of attribute values of similar items to the first item wherein the outputted plurality of attribute values are descriptive of actual characteristics of the similar items and are displayed independently of any listing of the similar items themselves, and wherein the similarity explorer display includes an item detail area comprising information describing characteristics of the first item; output, together with the plurality of attribute values, a plurality of attribute selection controls, the attribute selection controls being selectable by the user to select one or more of the attribute values; receive one or more selections of the attribute selection controls made by the user, thereby receiving an indication of one or more of the attribute values selected by the user; retrieve, in response to receiving the one or more selections of the attribute selection controls, a subset of the similar items that are similar to the first item and that share the one or more selected attribute values; and output the subset of the similar items, thereby enabling the user to visually compare the first item with the subset of similar items.