Big Ben and houses of parliament Depth of Field being used creatively - I feel this gives a much better effect than having shot the image with a smaller aperture which would give a bigger focus in the image (so Big Ben in the background would have been in focus too).
Your ultimate photography cheat sheet guide. Complete with info about aperture and how it relates to depth of field, shutter speed, ISO, and exposure. All the essentials. http://www.photo-geeks.com/understanding-exposure/
Autumn tree: I like the angle of this shot because it enhances the trees large size. Additionally I like the shallow depth of field, focussing the lower leaf yet enhancing its colour with the out of focus background.
Michael Penn - Philadelphia 471 In this photo the aperture was low to create a depth of field. It has a bokah effect where the background is blury, creating a sharp, focused effect on the phone. The shutter speed I imagine was on a low setting, capturing the movement in the background therefore inhancing the stillness and mystery of the abandoned phone.