A test shortcode plugin that outputs the most recent posts, while not stomping the current loop.

recent-posts-shortcode-test.php

<?php
/*
Plugin Name: Recent Posts Shortcode Test
Author: Mark Jaquith
Author URI: http://coveredwebservices.com/
*/

class CWS_Recent_Posts_Shortcode_Test_Plugin {
	static $instance;
	private $id;
	private $post;

	public function __construct() {
		self::$instance = $this;
		add_shortcode( 'recent-posts', array( $this, 'recent_posts_shortcode' ) );
		add_shortcode( 'foo', array( $this, 'foo_shortcode' ) );
	}

	public function recent_posts_shortcode() {
		global $post, $id;
		// Stash the current state of $post and $id, since we're going to overwrite them
		$this->post = $post;
		$this->id = $id;
		// Most recent 5 posts, with recursion prevention
		$q = new WP_Query( array( 'posts_per_page' =>5, 'post__not_in' => array( $id ) ) );
		$return = '';
		while( $q->have_posts() ) : $q->the_post();
			$return .= '<hr /><h3>' . get_the_title() . '</h3>' . apply_filters( 'the_content', get_the_content() );
		endwhile;
		// Restore $post and $id
		$post = $this->post;
		$id = $this->id;
		return $return;
	}

	public function foo_shortcode() {
		return "FOO SHORTCODE";
	}

}

// Bootstrap
new CWS_Recent_Posts_Shortcode_Test_Plugin;