Statistiques de fréquentation en français

Mediametrie e-stats - statistiques de fréquentation des principaux sites français

Nielsen-netratings.com - Statistiques de fréquentation internet en France (Suisse également disponible)

Outils internationaux de fréquentation

Alexa.com - Free service that assesses the traffic of any website, offered by Amazon inc.
Ranking.com - Online popularity of the most visited websites.

Quantcast.com - Free traffic assessment, but reliable only for the medium & large US domains & websites.

Compete.com - Assessment of traffic for any website.

Nielsen-netratings.com - Statistics about internet usage & websites visited in selected countries. Great but very expensive paying version.