Here's what i use. It doesn't leave any chopped word on the end.
Very handy for long strings..

<?php 
function do_TrimString($string, $MaxSTRLEN = null) {
    if ($MaxSTRLEN == null) { global $MaxSTRLEN; }
    if (strlen($string) > $MaxSTRLEN) {
        $string = substr($string, 0, $MaxSTRLEN);
        $end = strrpos($string, ' ');
        if ($end === false) {
            $end = $MaxSTRLEN;
            }
        $string = substr($string, 0, $end) . '...';
        }
    return $string;
    }
?>