DPReview has a sample image at every ISO from 50, to 102400. They describe the shooting conditions here. Choose an ISO. Click the image twice to get to full size.

Just as a non-scientific "looks like it to me", the 51200 shot, looks like my T1i's 3200, which is pretty amazing.

Oh, and for the official Canon shots, Bryan has the English page in his news feed, but on page 4 of the Australian store leaking the 5DmkIII thread, there is this link to the Japanese samples page, which has a few more shots available, such as the ISO3200 tiger and wedding shots, which are marked as 'Coming Soon' on the English page.

edit: Added link to Canon Japanese samples