I use this program to scramble my passwords and passphrases.
http://cdn.simtel.net/pub/simtelnet/win95/secmisc/Override.zip
It has an option to set up a password scrambler. What you do is type
in a chosen password into a password box, then double click the
password to highlight it, then you press an Fn key which converts the
password to an MD5'ed password, and then pasting it back into the
password box. It works well. The origional password you enter could
simply be the site name, its url, the first word on a site's page, etc.
There is an option to append a constant to your chosen password to
keep it unique to your system. There was some discussion on a science
site about it where someone was saying that there was not that much
more enthropy to the scrambled password, but the program does make
password remembering easier and eliminates having to look one up for
each site.
Someone is in the process of creating something like this as an addon
for FireFox.