Sketches: Grinning Demon - See the development of the art of Ol' Grinny.
Onslaught wallpaper and screensavers - A Grinning Demon desktop wallpaper is featured as one of the goodies linked from the Onslaught product page.
Sketches: Havoc Demon - Check out how the look of the Thomas Baxa demon came to be.
The new look of tokens - A peek at token promo cards in the new card face, featuring the Promise of Power demon token.
And now let's add to the list -- here's a new demonic tidbit for today.
Mirrodin Demon Horns
Although they were painted by three different artists, the look of demon horns in Mirrodin block is very consistent. Compare the jagged, curving horns of Reiver Demon, the Promise of Power token card, and of course, Demon's Horn: