Get first paragraph from a WordPress post.

get-fisrt-paragraph.php

<?php
/**
 * Get first paragraph from a WordPress post. Use inside the Loop.
 *
 * @param	$class	string optional class name to include in the paragraph
 * @return  	string
 */
function get_first_paragraph( $class = '' ){
	global $post;
	
	$str = wpautop( get_the_content() );
	$str = substr( $str, 0, strpos( $str, '</p>' ) + 4 );
	$str = strip_tags($str, '<a><strong><em>');

	return '<p class="' . $class . '">' . $str . '</p>';
}