Yahweh:Michael Clarke Duncan - talented actor who I think could capture the way Yawheh flips from "god who wuvs you" to "FEAR MY WRATH!!! BWAHAHAHAHAA!" very well and make the latter genuinely scary.
Helen Mirren - I think she could do a very good cold, imperious Yahweh.
Anthony Hopkins - Reprise his performance as Hannibal, but with magic powers.
George Takei - Did a pretty good job of being lofty and forbidding in
Heroes. I think he could get Yahweh's ruthlessness down.
John Noble - My favorite. Played Walter Bishop on Fringe, would be awesome because of the way he can portray a seamless blend of menace and personal presence with bumbling absent-mindedness and madness (hence all those Biblical contradictions and iron chariot class fails).
Jackie Chan - For a more comedic-oriented film with some physical slapstick and perhaps martial arts, emphasizing Yahweh's bumbling side over his viciousness.
John Malkovich - Does creepy psychopath very well.
Satan:Wesley Snipes - I picture him as a very "cool" Satan.
Jada Pinkett Smith - Would do a good job as an intense, fierce rebel leader.
Jude Law - Great as a cunning, "tempter" type.
Angelina Jolie - Has the range to cover both "temptress" and "fierce rebel" (action/combat) aspects of the role.
Zhang Ziyi - Opposite Jackie Chan in the comedic/martial arts version. Grace and beauty (see Ezekiel 28).
Captain Robert from Abney Park - I have no idea if he can act, but he has buckets of charisma. Plus, Satan as a Prometheus "giver of forbidden knowledge to humankind" figure with brass goggles, airship pirate duds, and clockwork gadgetry...
yeaaaah.
As both ("Oh God, You Devil" style):Alan Rickman - 'Nuff said.
Angelina Jolie - I think she could do Yahweh also, with some special effects makeup to age her a little.