How can I bypass governmental censorship of certain websites, for instance in Iran?

There are a number of different ways to bypass government bans on websites. And one of them is Tor Browser.

Further information can be obtained from: www.torproject.org

And download options are here: www.torproject.org/projects/torbrowser.html.en

EDIT: Although it's fairly straightforward as this Tor Browser Bundled runs as a portable tool, a PPA channel might also come very handy, at least for automatic updates:

• https://launchpad.net/~upubuntu-com/+archive/tor
• https://launchpad.net/~upubuntu-com/+archive/tor64

While Tor is an easy way, it is soooo slooow. The better one would be an SSH tunnel. Mass block of SSH is nearly equal to mass block of Internet. You can easily create your own SSH Tunnel gate on any server abroad that you own. There are even some free tunnel providers, but beware of scams.