Brandon Keim over at Wired Science has compiled a list of some of "the most interesting animal tool use yet observed".
http://blog.wired.com/wiredscience/2009/01/animaltools.html
...after digging a water hole, elephants will strip bark from a tree, chew it into a ball, then use it to fill the hole. Once the top has been covered with sand, the elephant has an evaporation-resistant canteen.
http://blog.wired.com/wiredscience/2009/01/animaltools.html
Bales of hay had been stacked 10feet beyond their outdoor enclosure and the bull decided he REALLY wanted it. He studied the situation (you could see him working the problem) and tried everything he could to get the lever between the gate and the padlock chain.
He tried everything he could but did not have the dexterity and could not get the leverage he needed to pop it. He finally got frustrated and gave up, but it was fascinating to watch him actually fashion a tool.
(BTW: this was when the zoo was run by Jack Hannah who we had seen working with them since he was a teenager.)