Ghostery is your window into the invisible web – tags, web bugs, pixels and beacons that are included on web pages in order to get an idea of your online behavior. Ghostery tracks the trackers and gives you a roll-call of the ad networks, behavioral data providers, web publishers, and other companies interested in your activity.
Available as extensions for Chrome, Internet Explorer, Firefox and Safari, Ghostery also lets you block the trackers it finds, and view the source of suspect scripts. Running it is quite an eye-opener, to say the least.
Really cool to see what websites are really running on your computer!