You might want to check out the pwgen application. I know it to be available in the Ubuntu, Fedora, Debian and Suse repositories.
From the man page:
The pwgen program generates passwords
which are designed to be easily
memorized by humans, while being as
secure as possible. Human-memorable
passwords are never going to be as
secure as completely completely random
passwords. In particular, passwords
generated by pwgen without the -s
option should not be used in places
where the password could be attacked
via an off-line brute-force attack. On
the other hand, completely randomly
generated passwords have a tendency to
be written down, and are subject to
being compromised in that fashion.
The pwgen program is designed to be
used both interactively, and in shell
scripts. Hence, its default behavior
differs depending on whether the
standard output is a tty device or a
pipe to another program. Used
interactively, pwgen will display a
screenful of passwords, allowing the
user to pick a single password, and
then quickly erase the screen. This
prevents someone from being able to
"shoulder surf" the user's chosen
password.