Unfortunately, all the good ones of the olden days have ceased to be, or at the very least require money/login/password. If you know of new anonymizing proxies, send me a mail.

Encrypting Anonymizers - Provide high security against 3rd-party snoops. May also bypass certain censorware products.

The Cloak (http://www.the-cloak.com/) encrypting anonymizer. (Requires Javascript and cookies.)

Anonymous Surfen (http://www.anonymsurfen.com/) anonymizer with SSL encryption option. (May not work with systems that change IPs or user-agent string with each request.)
 

Proxy Servers - Not high-grade security, but it will hide your identity from the remote site, e.g. stop your competitors from knowing who's checking up on them.
 
AnonymProm - free/pay anonymizing proxy.

IDZap (www.IDZap.com) Requires email address to sign up. 

Guardster - Ad frame.
  
Anonymizing Software
 
JAP (English/Deutsch) - Software for your computer that passes your Internet requests through a chain of encrypting relay servers.