The character window is the actual in-game interface window that opens when you hit the "C" key. It shows your character's name and class, along with all of their essential stats; attributes, resistances, damage, armor, to/hit, and much more.
Other Interface elements:
Character window circa October 2010.
Though the Character window has been seen in every demo build of the game, at Blizzcon in 2008, 2009, and 2010, Blizzard has never released a screenshot of it, nor shown it in any of the official gameplay movies. (They've shown other interface windows repeatedly.)
The only images of it are those seen in shaky-cam videos from game conventions. The most recent, and a fairly good view, comes from Blizzcon 2010, and can be seen to the right. This image has been modified; the unreadably-blurry text has been swapped out with text typed in via photoshop. This doesn't look as pretty as the in-game image, but at least it's legible.
Unlike the ever-changing inventory window, the basic form of the character window has changed little during the game's development. It's always listed the attributes, resistances, damage, defense, and other essential stats. The presentation has evolved, and continues to do so, but the content is fairly set.
Note that there's a lot more info than there was in Diablo II, and that the numbers go to decimal places, presenting the information in far more detail than in earlier games in the series.
Media
Other elements of the game interface can be seen in the Interface Screenshots gallery. Much higher quality images of the character window will be made available as the game nears release.
Blurry cam view of the Character window.
