This one is crazy with magento because sometimes it works and sometimes it just shows blank page. Once it gave me a real hard time. Finally found solution somewhere.
//I just had to do was add ->debug() //on the object that i wanted to print as: $obj->debug(); //e.g. if i had $_cart = Mage::getModel('checkout/cart'); //to use print_r or var_dump, i needed to do print_r($_cart->debug());
These are methods available for a product: