The second one behind Yahoo, probably due to more severe filtering. A very strange movement lead this formerly well-known and pioneer database to be one of the leaders in the group of the large indexes. It offers statistical data for each website from Alexa. Indexing by site, not page. Another portal with a directory.
Quality is a criteria in the selection of sites.
It is not possible to check that it covers 2 million websites. A different approach, with thematic areas maintained by a different expert. A very experimental service, with a hierarchical search system. Very well covered the section about Information Science, although coverage of other quality academic resources is also good. Webliography maintained by Louisiana State University Librairies.