Mediatraffic/United World Char, the first and more reliable source for worlwide figures for albums and tracks
UKmix forums - Chart Analysis, the biggest charts forum
Pulse forum - General Music News, good section with a lot of charts and sales info, especially for USA
Haven forum - Charts, good for charts and sales info, especially for UK
this page Buzzjack forum - Chart chat, good chart forum
Billboard, the official USA chart site based on Nielsen/Soundscan data
MusicWeek, the official source for UK charts and sales info.
Site about Sales in France, other sales estimations and more.
Site with a searchable database of chart-run of different countries
Collection of sites for different countries (12) with weekly chart archives.
Biggest French community about charts, sales and music