Flector

Truncate Comments is a plugin that hides a part of a long comment under a “Read more” link that, when clicked, reveals the hidden part of the comment. The plugin provides the functionality of Amazon.com comments.
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The plugin uses <a href="http://www.aakashweb.com/jquery-plugins/collapser/" rel="nofollow ugc">jQuery Collapser</a> by Aakash Chakravarthy.

Truncate Comments

The plugin uses Javascript to hide long comments (Amazon-style comments).

You can use this plugin to hide part of the text of a post in a nicely-formatted container that will becomes unhidden when clicked on. The plugin can be useful for creating FAQ pages, hiding large pictures, and things like that.
The plugin creates its own “Spoiler” button in the visual editor, but you can also add spoilers directly using tags. For example:
<pre><code>[spoiler title='Title']Spoiler content[/spoiler]
</code></pre>
or
<pre><code>[spoiler title='Title' collapse_link='no']Spoiler content[/spoiler]
</code></pre>
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BBSpoiler

This plugin allows you to hide text under the tags [spoiler]your text[/spoiler].

Truncate Comments vs BBSpoiler