debug mode

functions.php

/* Generates current template file name - For debugging only! */
add_filter( 'template_include', 'var_template_include', 1000 );
function var_template_include( $t ){
    $GLOBALS['current_theme_template'] = basename($t);
    return $t;
}

function get_current_template( $echo = false ) {
    if( !isset( $GLOBALS['current_theme_template'] ) )
        return false;
    if( $echo )
        echo $GLOBALS['current_theme_template'];
    else
        return $GLOBALS['current_theme_template'];
}

header.php

<div><strong>Current template:</strong> <?php get_current_template( true ); ?></div>