CECID
CECID (and its client FLACCID) are anonymisers that remove tracable information and bounce a request off several other clients in a decentralized P2P anonymisation network.

Domain Forte
Anonymous Web surfing via CGI proxy

iPrive.com
Web-based privacy enhancing proxy service. Offers URL encryption, advertisement blocking, anonymous email and an IE toolbar.

Proxy Stealth Tests
These tests will allow you to check to see if your proxy is anonymous.

Proxy Web Servers in Libraries
Presentations and surveys describing the uses of proxy servers (free and commercial) to solve library networking problems such as speed and filtering.

Somebody Anonymizer
Commercial service provides proxy, enhanced DNS, privacy protection, anonymous surfing, anonymous mailing and anti-censorship services.