First of all, Canon has put all the images on the 5D3 sample pic page (click here). They can be downloaded so you can play around with them.
More high ISO pics can be seen on Paul Wards site, including crops and comparison with the 5D2:
- 5D2 vs 5D3 crop at ISO 3200 (click here)
- 5D3 crop at ISO 6400 (click here)
- 5D3 crop at ISO 25600 (click here)
The post has also a quick hands-on review and a HDR shot (click here, then scroll down).