Ghostery

Find out how web sites are watching you.

Ghostery alerts you about web bugs, ad networks and widgets on every page on the web.

Web bugs are hidden scripts that track your behavior and are used by the sites you visit to understand their own audience.

"..does what none of the most expensive antispyware programs that I know are capable of..."

Firefox Add-on for Windows, Mac or Linux.

No adware, spyware, or malware.
Ghostery is free to download, free to use, and does not contain any adware or spyware.