I'd submit that anything that satisfies the entrance requirements of the SohoPhoto Krappy Kamera competition fits the category--

http://sohophoto.com/krappy_kamera_comp.html

They don't necessarily have to be toys, and there's a question of whether Dianas and Holgas were literally intended originally to be toys or just as inexpensive cameras manufactured from cheap materials, but I think there's an aesthetic there. The idea is to make an interesting photograph with a camera that doesn't necessarily give the user much technical control and may even introduce artifacts that are beyond the user's control. It's about giving chance a greater role in the production of art.