The Webometrics Ranking of World Universities is an initiative that tries to establish which universities provides to most content on the web and get visibility from it. The ranking of universities is based on the size of the web domain (20%), the number of rich files available (PDF, RTF, etc., 15%), Research on Google Scholar (15%), and link visibility (50%). Not surprisingly, US universities monopolize the 24 first spots, led by MIT.
Webometrics also ranks repositories, the criteria being the same as for universities. The ranking is led by Arxiv, the grand-daddy of all repositories covering much of Physics and Mathematics. RePEc is number 2, followed by E-LIS, a repository in Library Sciences founded by Thomas Krichel, who is also at the origin of RePEc!
Other notables down the list: HAL, a French repository that feeds to RePEc at number 9, CDLIB, the University of California Repository, a RePEc participant at number 19, SSRN, not in RePEc, at number 37, the Munich Personal RePEc Archive, barely a year old, is already number 56, and AgEconSearch, not in RePEc, is ranked number 126.