Diceware is a scheme for generating passwords, created by Arnold G. Reinhold in August of 1995. Arnold's original page describing the process is – surprisingly – still around and – more surprisingly – still updated regularly. This tool will generate diceware passwords for you, but with some subtle differences.
Firstly, I'm using the EFF's "Enhanced" Wordlist for diceware; it replaces many of the rare and unusual words in Arnold's original list with words that are slightly longer but easier to remember.
However, some words in the EFF's list are product or company names, so I have replaced these as follows:
I may have missed some, so please let me know if you come across any others.
The second difference is that Arnold suggests using a wordlist with a length that is a power of two generating diceware passwords by machine (and even provides a list with 8,192 words). I decided that I preferred the EFF's list and that any benefits from even powers of two and the slight loss in entropy to be acceptable.