Displaying all Custom fields on post except some

You will have to walk/map/filter the array before printing them. There’re plenty of array_*() functions provided by PHP for that. Example:

$custom = get_post_custom();

// Remove all strings starting with `_`
array_filter( $custom, function( $data, $name ) {
    return "_" !== substr( $name, 0, 1 );
}, ARRAY_FILTER_USE_BOTH );

foreach ( $custom as $field )
    var_dump( $field );