Retrieve bestsellers

Here is how you can retrieve a list of bestsellers

$collection = Mage::getResourceModel('sales/report_bestsellers_collection')
            ->setModel('catalog/product')
            ->addStoreFilter(Mage::app()->getStore()->getId())//if you want the bestsellers for a specific store view. if you want global values remove this
            ->setPageSize(5)//se there the number of products you want returned
            ->setCurPage(1);
foreach ($collection as $_product){
    $realProduct = Mage::getModel('catalog/product')->load($_product->getProductId());
    //do something with $realProduct;
}

Make sure you refresehd the statistic for bestsellers. Reports->Refresh statistics. Select refresh lifetime statistics for bestsellers. Enjoy.