seanbdurkin

I recommend against using this plugin with the WordPress Visual Editor, as I have not tested it with the visual editor, and will not support the use of the plugin through the Visual Editor.
Nice features of SBD Aside include:
<ul>
<li>HTML 5 Support. SBD Aside uses the HTML 5 semantic tag <a href="http://html5doctor.com/aside-revisited/" title="Aside element" rel="nofollow ugc"><code><aside></code></a> to play well with search engines and content aggregators.</li>
<li>Choose left or right placement on the page.</li>
<li>Choose expanded (“open”) style, or collapsible.</li>
<li>collapsible ones like on the top right of this page can be collapsed or expanded by the reader as required.</li>
<li>Choose round corners or square cut.</li>
<li>Choose background colour.</li>
<li>Choose width in pixels or percent.</li>
<li>Choose from one of two caption underline styles.</li>
<li>Display a caption</li>
<li>All of the above options/settings are optional. Define your own defaults in the plugin’s setting page.</li>
<li>The styling for the aside is compact, with a small font and low margins. This minimises space disruption to the main article.</li>
</ul>

SBD Aside

The SBD Aside plugin is a WordPress plugin that allows bloggers to easily create small side-bars for there entries, called asides.

dreamreal

Often, when a long block of text is being written, secondary content not 
germane to the paragraph in question is relevant, but out of scope of a 
given paragraph.
<pre><code> For example, this is text explaining that the author is using
 far too many words to be useful.
</code></pre>
This plugin allows users to write [aside]commentary[aside] and have it 
rendered appropriately.
<h3>History</h3>
Version 1.0 
 – First release

Insert Callout

Adds a sidebar comment (an inline box that includes commentary text) to a post

SBD Aside vs Insert Callout