BFilter is an ad-filtering web proxy featuring an effective heuristic ad-detection algorithm.
Powerful and sophisticated proxying filter. Allows you to influence the heuristic analyzer using URL hints; includes documentation and sample hints which made fixing issues a no-brainer. Code could use an upgrade. Wasn't able to compile it.
Needs work. Detects some Amazon thumbnail images and some reCAPTCHA captcha images as ads. Had to turn it off.