A recent article in the journal Current Biology by Dr Julian Finn from Australia's Museum Victoria and a group of researchers describes individual veined octopuses (Amphioctopus marginatus) using halved coconuts as shelter. This is being cited as an example of tool use. There's a fair amount of video coverage of the behavior from footage filmed between 1999 and 2008 off the coasts of Northern Sulawesi and Bali in Indonesia. I've linked to two below, and there's an ever better example embedded in this BBC article about the phenomenon.

Octopuses are amazing, lovely creatures, known for being escape artists who manage to evade aquarium staff, as well as their uncanny ability to mimic objects around them; I'd argue that the way this octopus uses seaweed counts as an example of tool use.