Tilt-shift photography is a creative and unique type of photography
in which the camera is manipulated so that a life-sized location or
subject looks like a miniature-scale model. To add good miniature effect to your photographs, shoot subjects
from a high angle (especially from the air). It creates the illusion of
looking down at a miniature model. A camera equipped with a tilt-shift
lens, which simulates a shallow depth of field, is essentially all you
need to start.
For those interested in more, Smashing Magazine has a great article with 50 beautiful examples of tilt-shift photography. There is a tutorial on tilt-shift photography at Tilt-Shiftphotography.net, of all places.