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.

Ross Cornell

This plugin adds a simple widget that allows you to display a number of recent blog posts from a specific category. You have the options to choose a title, category, number of posts and whether or not to show the post date. The posts will be ordered by date just like the default Recent Posts widget included with WordPress.

very easy to use

Very usefull

Just like the default Recent Posts widget except you can choose a category to pull posts from.

Recent Posts Widget Unlimited vs Recent Posts by Category Widget