JonDo (free) anonymizes your connections using a proxy service, so that a Web site or other Internet destination won't be able to see where you're really coming from. But while the software is free, and there's also a free level of service, it'll still cost you a good deal of connection speed.
To use the service, you first install the JonDo software on your PC. Next, you can either manually configure a proxy-compatible program (such as a Web browser) to use it, or pick up the JonDoFox download to automatically set up Firefox. JonDoFox creates a new Firefox user profile that's already set up for use with JonDo, and also has a number of privacy and security themed browser add-ons.
Once installed, your JonDo-enabled Internet connections are sent through multiple online "mix" servers, via multiple encrypted connections, to hide your PC's IP address. When your connection is finally passed along to the Web site in question, it will look like your request came from the final mix server, rather than your home PC. While that's good for privacy and anonymity, having to take all those extra network hops through mostly European-based servers means your surfing will take noticeably longer.
JonDo is surprisingly quick and easy to install, and includes a nice Assistant to help with first time set-up and testing. If you let it know that your connection is too slow, it will suggest choosing another service to see if that might help. Doing so did help in my testing - but the connection was still noticeably slow. A for-pay level of premium service promises faster connection speeds, and costs from 2 Euros for 200MB of traffic on up through 40 Euros for 6500MB.
If you're after maximum privacy for your surfing, JonDo can help with a minimum of fuss. Use it along with Firefox add-on JonDoFox to sweep a big broom across your online tracks--just remember that you'll be cruising about much more slowly.