WebsiteOutlook.com, whose figures on economic worth and daily pageviews I reported in LRC vs. the Beltway, lists almost all websites. Here are some conservative and libertarian think-tanks and educational organizations, ranked by daily pageviews according to WOC:

Mises Institute: 45,433
Heritage Foundation: 43,562
Cato Institute: 27, 186
American Enterprise Institute: 9,507
Heartland Institute: 8,102
Foundation for Economic Education: 5,247
Institute for Humane Studies: 4,596
Reason Foundation: 3,121
Claremont Institute: 2,514
Mercatus Center: 717