Although I was obviously aware of different focal lengths and how they affect the field of view, I had never really thought before about a standard for my camera, or that it was the focal length at which everything appears similar in size to viewing by eye.
As my camera is a Canon 450D it has an APS-C sized sensor. I know from previous reading that this is smaller than a full frame/35mm camera and affects focal length.
I found that the focal length for 'standard' on my camera would be about 60mm. I have an 18-55mm lens and a 70-300mm so I couldn't find out exactly, but at 55mm the scene was very nearly the same as viewing naturally.
Here are the three pictures taken to test focal lengths. The first is at 55mm, the second is at 18mm and the third is at 300mm.