Canon has posted a gallery of images shot with the Canon EOS 5D Mark III. These images are available for download in JPEG (around 6.5 MB) and in full resolution (22.3-megapixel). The gallery shows a wide variety of photographies, from studio images to wildlife photography. But they all have something in common : they have been shot with the best lenses Canon can make, L-series lenses, like the EF70-200mm f/2.8L IS II USM, the EF50mm f/1.2L USM, the EF85mm f/1.2L II USM or the EF24-70mm f/2.8L II USM announced a few days ago.
Canon has also posted a few video samples with a behind de scenes video. Note that although the Canon EOS 5D Mark III is capable of recording Full HD 30p movies, you can only display 960 x 540 pixels samples.
Here the link to the Canon EOS 5D Mark III sample image page on Canon global website.
UPDATE : Canon EOS 5D Mark III review available.