Helpero recommends Torpark.

Hacktivismo, an international group of computer security experts and human rights workers, just released Torpark, an anonymous, fully portable Web browser based on Mozilla Firefox. Torpark comes pre-configured, requires no installation, can run off a USB memory stick, and leaves no tracks behind in the browser or computer. Torpark is a highly modified variant of Portable Firefox, that uses the TOR (The Onion Router) network to anonymize the connection between the user and the website that is being visited.

Every few minutes, the Torpark browser causes a computer's IP address to appear to change. IP addresses are numeric identifier given to computers on the Internet. The number can be used along with other data to potentially track down a user, as many Web sites keep track of IP addresses.

One minor downside is that surfing with Torpark is slower than with a typical browser over the same connection.

You can download Torpark from here.

Another good example is Browzar.

If you want to surf the Internet without leaving a trace of your surf history, Browzar is the new solution.

Based on Internet Explorer engine, Browzar offers no browsing history, stored files, or cookies no embarrassing search auto-complete, no installation - Just click 'run' and go and no registration required.
You can download Browzar as many times you want, whenever and wherever you need it to protect your privacy.

You can download free Browzar from here.