Not So Weak Passwords for Chrome
More About Not So Weak Passwords
It's GPL, you can find the code at https://github.com/mapio/nswp
It is well known that reusing the same passowrd on different site is very dangerous, as well as using weak passwords; on the other hand, is quite difficult to remember many different good passwords.
The idea behind this extension is very easy (and not new at all): to generate a password concatenate a (unique and strong) secret, or "master password", to the web site URL (or something derived from it) and then take (ten pass of) the SHA1 of it.
In more detail, once you've set your secret in the extension options, by clicking on the extension icon you get a dialog with two fields: the first contains the host portion of the current tab (omitting the 'www.' prefix, if present) and the second one the generated password that will be automatically copied to the clipboard. If you want to edit the first field (for instance, to add a prefix to identify different accounts), just do it and the password will be automatically re-generated (an copyed to the clipboard).