The nonk 6

xB Browser -- Download | 
Description: "A portable version of Firefox with a well integrated Tor engine that uses the free Tor network. It's easy to setup and doesn't require advanced knowledge, but you will have to use it as a second browser for anonymous surfing in contrast to Vidalia or JonDo that also support normal browsing." (Creates an empty folder in the user profile.)
The drawback to xB Browser is that it's browser specific to Firefox. Users who prefer to use a different browser, can try JonDo. JonDo works with other browsers, but you may have to follow guides to get all the settings right. But JonDo also recommends a Firefox solution:
Another option is to use a Portable Firefox with the JonDo-Portable service and the JonDoFox configuration. The advantage is that the JonDoFox configuration comes with many other specially selected security addons (NoScript, CS-Lite, Adblock Plus), installs as an alternate profile (allowing you to switch between normal and anonymizing profiles), and allows proxy switching between the Tor or JonDo anonymizing networks. However, the JonDo-Portable service requires Java and is more resource intensive.