Mike

As a logged in user, you can already control the visibility of the WordPress Toolbar when modifying your profile with the ‘Show Toolbar when viewing site’ option. This plugin lets you manage that option while viewing the public part of the site without visiting your profile page saving you a few steps. A few steps over the course of a year can be a considerable saving.
To use, add the following to the end of your URL location:
<ul>
<li>?hidebar or ?nobar to hide the Toolbar</li>
<li>?showbar or ?yesbar to show the Toolbar</li>
</ul>
If you have a ? in the URL already, swap it with a &
This plugin differentiates itself by having a zero footprint. It does not leave any visible buttons, add any extra javascripts or CSS styles. It is also WordPress Network compatible – that is, you can enable it network wide.
Collaborate, participate, or fork this plugin on <a href="https://github.com/zedzedzed/toggle-toolbar" rel="nofollow ugc">Github</a>.

Toggle Toolbar

Easily toggle the WordPress Toolbar by adding commands to the end of your URL while logged in.

jugheadjones

Puts a small button on the top right corner of pages for logged in users to show/hide the WordPress toolbar.

Wolfen Toggle Bar

Makes the default WordPress admin bar toggleable.

Toggle Toolbar vs Wolfen Toggle Bar