[Air-l] good source for web traffic data

Hi, I am looking for a good on line source for web traffic data on individual sites (including, but not only, weblogs). As far as I know, there is www.alexa.com, which provides rankings and users estimates based on its toolbar's users. Does anyone know of a more reliable source? Thanks, Cristian Vaccari www.cristianvaccari.it www.comunicarepolitica.it