Although the standard commercial version of the Blu-ray release will probably have the same poster image of Batman standing in front of a building emblazoned with his logo, we've received an image of a Blu-ray cover featuring an image of Heath Ledger's Joker, and we also have a look at the insert of the Special Edition Blu-ray, which will be available at the same time.
UPDATE: We just received some more images of covers for the standard Dark Knight Blu-ray, as well as the packaging for a 2-Disc Batpod Limited Edition, from BDS23420:
2-Disc Batpod Back Cover
Blu-ray Front Cover
Blu-ray Back Cover
Both Blu-ray Covers
If that isn't enough Dark Knight Blu-ray goodness, here's and advertisement for the DVD and Blu-ray release:
Dark Knight is scheduled to be released on DVD and Blu-ray on December 9, 2008, and though it's not available to pre-order yet, you can keep an eye on it Amazon.