get-fisrt-paragraph.php

<?php
/**
 * Get first paragraph from a WordPress post. Use inside the Loop.
 *
 * @return string
 */
function get_first_paragraph(){
	global $post;
	
	$str = wpautop( get_the_content() );
	$firstP = strpos( $str, '</p>' );
	$secondP = strpos( $str, '</p>', ($firstP + 1)
	$p1 = substr( $str, 0, $firstP + 4 );
	$p2 = substr( $str, ($firstP + 4), $secondP);
	
	$p1 = strip_tags($p1, '<a><strong><em>');
	$p2 = strip_tags($p2, '<a><strong><em>');

	return '<p>'.$p1.'</p><p>'.$p2.'</p>';
}