WordPress Excerpt _with_ HTML tags. Based on some brilliant snippets elsewhere.

functions.php

/**
 * Close out any open tags
 * via: http://milianw.de/code-snippets/close-html-tags
 */
function closetags( $html ) {
	#put all opened tags into an array
	preg_match_all('#<([a-z]+)(?: .*)?(?<![/|/ ])>#iU', $html, $result);
	$openedtags = $result[1];

	#put all closed tags into an array
	preg_match_all('#</([a-z]+)>#iU', $html, $result);
	$closedtags = $result[1];
	$len_opened = count($openedtags);
	# all tags are closed
	if (count($closedtags) == $len_opened) {
	return $html;
	}
	$openedtags = array_reverse($openedtags);
	# close tags
	for ($i=0; $i < $len_opened; $i++) {
		if (!in_array($openedtags[$i], $closedtags)){
			$html .= '</'.$openedtags[$i].'>';
		} else {
			unset($closedtags[array_search($openedtags[$i], $closedtags)]);
		}
	}
	return $html;
}

/**
 * via: http://aaronrussell.co.uk/legacy/improving-wordpress-the_excerpt/
 * @uses closetags
 */
function bookstoker_trim_excerpt($text = '') {
	$raw_excerpt = $text;
	if ( '' == $text ) {
		$text = get_the_content('');
		$text = apply_filters('the_content', $text);

		$text = strip_tags( $text, '<em>'); // Only allow emphasis

		$excerpt_length = apply_filters('excerpt_length', 55);
		$excerpt_more = apply_filters('excerpt_more', ' ' . '[&hellip;]');
	 	$words = explode(' ', $text, $excerpt_length + 1);

		if (count($words)> $excerpt_length) {
			array_pop($words);
			$text = closetags( implode(' ', $words) ) . $excerpt_more;
		}
	}

	return apply_filters('wp_trim_excerpt', $text, $raw_excerpt);
}

remove_filter('get_the_excerpt', 'wp_trim_excerpt' );
add_filter('get_the_excerpt', 'bookstoker_trim_excerpt');

I'm getting an odd bug where an extra p tag is surrounding the excerpt more text.