helpgeek

By default, the built-in Recent Posts widget in WordPress only allows you to 
display up to 15 recent posts max, even if you specify a larger number. This 
is hard-coded into the WordPress core so any modifications you make would have 
to be redone upon every WordPress update.
No longer!
The Recent Posts Widget Unlimited functions exactly as the built-in WordPress 
widget but without the 15-post restriction. You can now specify an unlimited 
number of recent posts to display without resorting to modifying the WordPress 
core.

pjgalbraith

An advanced version of the WordPress Recent Posts widget allowing increased customization.
Features Include:
<ul>
<li>Display post thumbnails, with customizable size.</li>
<li>Display post excerpt, author, comment count, and more. </li>
<li>Provides options to trim the number of characters in the title and excerpt.</li>
<li>Override the post order to order by; date modified, title, post ID, random, comment count etc.</li>
<li>Exclude or include specific posts, authors, tags, or categories.</li>
<li>Also includes a simple template parser so you can override the default output making custom styling easy.</li>
</ul>
<h3>Documentation</h3>
See documentation at http://www.pjgalbraith.com/2011/08/recent-posts-plus/

Recent Posts Widget Unlimited vs Recent Posts Plus