I stumbled upon the YourWebSiteValue.com resource, which allows you to find out the value of a site, based on the popularity of the site in search engines, its quality and other factors. Small selection:
Site
Cost of
habrahabr.ru
127 742 $
mail.ru
37 003 222 $
yandex.ru
26 047 449 $
dirty.ru
157 200 $
digg.com
$ 17,368,372
twitter.com
7 955 $ 457
I don’t try to judge the objectivity of these prices - after all, the assessment is made by a machine on the basis of sometimes invisible (as in the case of “quality”) factors, but it may be useful to someone as an argument in the negotiations.