Enter random junk from the keyboard. This page will use your keystrokes, the times between the keystrokes, and randomness from your operating system to key a random number generator. We then use this randomness to select combinations of words from the dictionary, whose combinations will have no inherent meaning. Choose the amount of password entropy you want, and we'll pick the number of words requeired accordingly.
All computations are done in your browser; check your debugging tabs to see that no network traffic occurs after the initial page load.