wp_kses() will do what you need. You need to tell it what tags to allow. Alternatively use wp_kses_post() which allows anything you can add to a post. This one may not be strict enough for user input though so I'd suggest going with the first.
echo wp_kses( $text, array(
'a' => array(
'href' => array(),
'title' => array()
),
'br' => array(),
'em' => array(),
'strong' => array(),
) );
http://codex.wordpress.org/Function_Reference/wp_kses http://codex.wordpress.org/Function_Reference/wp_kses_post