lx6g

You can choose from upper and lower letters, digits and special characters to make your new hardcore passwords impossible to break. 
And yes, all the passwords are generated only within client’s browser session and are not saved anywhere on the server side, 
so it is absolutely safe to use in real world.
You can also specify the following attributes to tune the form’s appearance:
<ul>
<li><code>length=4..64</code> specifies the default length of a password. Allowed values range from 4 to 64. </li>
<li><code>upper=1</code> enables upper-case letters option. Activated by default.</li>
<li><code>lower=1</code> enables lower-case letters option. Activated by default.</li>
<li><code>digits=1</code> enables digits option. Activated by default.</li>
<li><code>special=1</code> enables special characters <code>,.:;_=</code> option. Disabled by default. </li>
</ul>
Plugin’s Official Site
<a href="http://lx6g.com" rel="nofollow ugc">Alex Granovsky Blog</a>

LX Password Generator

LX Password Generator is simple yet nifty password generation form to be placed in any page or post you like.

Budiony Damyanov

Tired to think about what should be the new password while creating or editing users? This small plugin will do the job for you. 
It generates and uses a random sequence of numbers and/or text or special characters in password fields during creating or editing users. The password is with variable length and can be generated on-the-fly (no page reload is necessary). It consists from lower letters, upper letters, numbers and/or special characters. To do that, go to <code>Users</code> and <code>Add new</code> one or edit existing one.

bodi0`s Password generator

Brain-free generation and usage of random sequence of numbers and/or text or special characters in password fields while creating or editing users.

LX Password Generator vs bodi0`s Password generator