Susan Cowsill may be the best-kept secret in Americana. Just ask the packed crowd at any one of her concert stops on the tour in support of her latest release, 'Lighthouse.' If you think the album's 12 songs -- including the much-heralded 'Avenue of the Indians,' on which she duets with old family friend Jackson Browne -- are powerful, wait until you hear Susan's husky, expressive voice in concert