Here is another fun spy gadget from the guys over at Chinavasion, The Screw Spy Camera.
As the name suggests, the camera is hidden behind what looks like a standard screw, and it can be mounted behind a wall or hidden so it looks just like a normal screw.
I am not sure how practical it would be, as it would be quite a lot of work to get it hidden behind a wall, also it wouldn’t be much use if someone decided to hang a picture on it.
If you want one, the 
Screw Spy camera is available for £29.34 about $48 from Chinavasion.