Arnold Ho shows on his blog how you can use Photoshop to make images look like miniature models:

miniature_1

Arnold also shows other examples of his technique on his matchbox toy car page, like this one:

Miniature

Arnold wrote a nice tutorial that explains how to make these miniatures.
Correction March 19 2006: it was actually Christopher Phin who wrote that tutorial.

He also added a tips page on which he shows how to make the miniatures look more realistic.

Well done Arnold for coming up with an original concept, supported by well written articles!