The upcoming 3.7 release of WordPress is getting a new password strength meter, using the zxcvbn library from Dropbox.
zxcvbn.js is 683 KB (minified). I’m simply not going to be able to convert this to PHP, and I can’t see anyone else taking the challenge on.
The new version isn’t up on the wordpress.org repository yet, but you can download it from GitHub. If anyone’s using the beta of 3.7, do please give it a whirl and let me know if there’s any issues. Any other feedback regarding this development is also most welcome.