template.tpl.php

<?php
/**
 * Theme_menu_tree doesn't provide any context information
 * THIS SUCKS
 * But you can use hook_block_view_alter to change the theme wrapper
 * OUF!
 */


function MYTHEME_menu_tree(&$variables) {
 return '<ul class="nav">' . $variables['tree'] . '</ul>';
}

function MYTHEME_menu_tree__menu_top_menu(&$variables) {
 return '<ul class="nav center">' . $variables['tree'] . '</ul>';
}
//main menu (top) using the menu block module
function MYTHEME_menu_tree__menu_block__2(&$variables) {
    return '<ul class="nav main-nav nav-horizontal">' . $variables['tree'] . '</ul>';
}
//main menu (level 2 sidebar) using the menu block module
function MYTHEME_menu_tree__menu_block__1(&$variables) {
      return '<ul>' . $variables['tree'] . '</ul>';
}
function MYTHEME_menu_tree__menu_block__1__level1(&$variables) {
    return '<ul class="nav nav-list">' . $variables['tree'] . '</ul>';
}


/**
 * Implements hook_block_view_alter().
 */
function MYTHEME_block_view_alter(&$data, $block) {
  // Check we get the right menu block (side bar)
  if ($block->bid == 'menu_block-1') {
    // change the theme wrapper for the first level
    $data['content']['#content']['#theme_wrappers'] = array('menu_tree__menu_block__1__level1');
  }
}