Remove WordPress Toolbar buttons

function mytheme_admin_bar_render() {
  global $wp_admin_bar;
  $wp_admin_bar->remove_menu('wp-logo');
}
add_action( 'wp_before_admin_bar_render', 'mytheme_admin_bar_render' );

For specific user roles you can wrap the add_action in a conditional, something like

if(current_user_can('editor')){
 add_action( 'wp_before_admin_bar_render', 'mytheme_admin_bar_render' );
}

http://codex.wordpress.org/Roles_and_Capabilities