wondermill

If you want to graphically display a random list of your posts with their featured image in the side bar, then this is the plugin for you. This plugin allows you to set the category IDs (or all categories) you want to pull the random posts from, the number of random posts to display, the maximum width and height of the featured image thumbnail, the widget title, and the colors of the surrounding box.

Random Posts with Thumbnails

Puts a list of clickable random posts with their featured image in your sidebar as a widget, this list is customizable.

RobMarsh

Random Posts displays a list of randomly chosen posts. The output can be customised in <a href="http://rmarsh.com/plugins/post-options/" rel="nofollow ugc">many</a> ways.
This plugin requires the latest version of the Post-Plugin Library: <a href="https://downloads.wordpress.org/plugin/post-plugin-library.zip" rel="nofollow ugc">download it now</a>.
<h3>Version History</h3>
<ul>
<li>2.6.2.0
<ul>
<li>new {imagealt} output tag — rather like {imagesrc}</li>
<li>{excerpt} can now trim to whole sentences</li>
<li>content filter can now take parameter string</li>
<li>widget can now take parameter string</li>
<li>output can be appended to posts & feeds</li>
</ul>
</li>
<li>2.6.1.0
<ul>
<li>the current post can be marked manually</li>
<li>widgets now honour the option to show no output if list is empty</li>
</ul>
</li>
<li>2.6.0.1
<ul>
<li>bug fix: installation code was failing on some systems</li>
</ul>
</li>
<li>2.6.0.0
<ul>
<li>version bump to indicate compatibility with WP 2.6</li>
<li>fix to really include attachments</li>
<li>new parameter for {imagesrc} to append a suffix to the image name, e.g. to get the thumbnail for attachments</li>
</ul>
</li>
<li>2.5.0.11
<ul>
<li>new option to include attachments</li>
<li>{php} tag now accepts nested tags</li>
<li>new output tag {authorurl} — permalink to archive of author’s posts</li>
</ul>
</li>
<li>2.5.0.10
<ul>
<li>fix for page selection in old versions of WP</li>
<li>made omit current post try harder to find current post ID</li>
</ul>
</li>
<li>2.5.0.9
<ul>
<li>new option to match the current post’s author</li>
<li>extended options for snippet and excerpt output tags</li>
</ul>
</li>
<li>2.5.0.7
<ul>
<li>new option to show by status, i.e., published/private/draft/future</li>
<li>{categorynames} and {categorylinks} apply ‘single_cat_name’ filter</li>
<li>fixes bug in WP pre-2.2 causing installation to fail</li>
</ul>
</li>
<li>2.5.0
<ul>
<li>{image} has new post, link, and default parameters</li>
<li>new {imagesrc} tag</li>
<li>fix to empty category bug</li>
<li>excluded posts bug fix</li>
<li>fix for intermittent bug with ‘omit current post’ option</li>
</ul>
</li>
<li>2.5b26
<ul>
<li>reverted thumbnail serving (speed)</li>
<li>fix current post after extra query</li>
</ul>
</li>
<li>2.5b25
<ul>
<li>option to sort output, group templates</li>
<li>removed ‘trim_before’ option added more logical ‘divider’</li>
<li>{date:raw}, {commentdate:raw}, etc.</li>
<li>fix for {image} resizing when and not </li>
<li>{image} now serves real thumbnails</li>
</ul>
</li>
<li>2.5b24
<ul>
<li>fix for recursive replacement by content filter</li>
<li>fix to {gravatar} to allow for ‘identicon’ etc.</li>
<li>fix to {commenter} to allow trimming</li>
<li>fix a warning in safe mode</li>
</ul>
</li>
<li>2.5b23
<ul>
<li>new option to filter on custom fields</li>
<li>nested braces in {if}; condition now taggable</li>
<li>improved bug report feature</li>
<li>better way to omit user comments</li>
</ul>
</li>
<li>2.5b22
<ul>
<li>fixes for tag bugs</li>
<li>show_pages option can now show only pages</li>
</ul>
</li>
<li>2.5b19
<ul>
<li>fix for content replacement filter</li>
</ul>
</li>
<li>2.5b18
<ul>
<li>fix output filter bug</li>
<li>new conditional tag {if:condition:yes:no}</li>
</ul>
</li>
<li>2.5b16
<ul>
<li>fix for {php}</li>
</ul>
</li>
<li>2.5b15
<ul>
<li>fix bugs, add ‘included posts’ setting</li>
</ul>
</li>
<li>2.5b14
<ul>
<li>fix file-encoding, installation error, etc.</li>
</ul>
</li>
<li>2.5b11
<ul>
<li>some widget fixes</li>
</ul>
</li>
<li>
2.5b9
<ul>
<li>clarifying installation instructions</li>
</ul>
</li>
<li>
<a href="http://rmarsh.com/plugins/random-posts/" rel="nofollow ugc">previous versions</a>
</li>
</ul>

Random Posts with Thumbnails vs Random Posts