Magento – How to get the attribute(manufacturer) Url Like example.com/brands/nike in magento

In addition to changing the URL which is being rendered, you'll need to rewrite Mage_Catalog_Model_Layer_Filter_Attribute::apply():

/**
 * Apply attribute option filter to product collection
 *
 * @param   Zend_Controller_Request_Abstract $request
 * @param   Varien_Object $filterBlock
 * @return  Mage_Catalog_Model_Layer_Filter_Attribute
 */
public function apply(Zend_Controller_Request_Abstract $request, $filterBlock)
{
    $filter = $request->getParam($this->_requestVar);
    if (is_array($filter)) {
        return $this;
    }
    $text = $this->_getOptionText($filter);
    if ($filter && strlen($text)) {
        $this->_getResource()->applyFilterToCollection($this, $filter);
        $this->getLayer()->getState()->addFilter($this->_createItem($text, $filter));
        $this->_items = array();
    }
    return $this;
}

$this->_getResource()->applyFilterToCollection($this, $filter) is where the ID is passed in. Your change needs to map the option text to the ID prior to this. Something along the lines of the following will get you going:

public function apply(Zend_Controller_Request_Abstract $request, $filterBlock)
{
    $filter = $request->getParam($this->_requestVar);
    if (is_array($filter)) {
        return $this;
    }
    $filter = $this->getAttributeModel()->getSource()->getOptionId($filter);
    $text = $this->_getOptionText($filter);
    if ($filter && strlen($text)) {
        $this->_getResource()->applyFilterToCollection($this, $filter);
        $this->getLayer()->getState()->addFilter($this->_createItem($text, $filter));
        $this->_items = array();
    }
    return $this;
}

I'm a bit concerned as to what effect this will have on caching, etc. but at least this will head you down the road to a solution.