Spamvert - Perl script for removing adverts and other things from web pages. Also known as abiprox. Only suitable for programmers. WebWasher - Sophisticated advert remover originally from Siemens , of all people. They employ 29 people on privacy related software, and make money from corporate clients buying an enterprise version.
Companies use it to remove adverts, reduce bandwidth and filter other undesirable content.
For Windows, Mac and Linux. Free for home and educational use. This proxy also provides caching, automated downloading, cache indices and security features. AdEater is currently a public proxy that you can use with any browser and OS, but it will slow down your browsing. Uses Muffin, which is described above.