Update II:
Apparently, there are forums for
Diablo IV,
Diablo V,
Diablo VI and
WarCraft IV: Ghost,
WarCraft V: Ghost,
WarCraft VI: Ghost as well...
Update:Earlier today, Blizzard added a ""
Diablo III General Discussion"" to the Battle.net forums.

Everything pieces together. Raise your hopes Diablo and Blizzard fans, your time has come.

It is the last day before the announcement and every Blizzard fan is going wild. Today Blizzard added to the ""hype-machine"" more clues:
Splash Screen

The ice opens wider, and the eyes are more clear now. These eyes really look like they belong to a Protoss, though nobody can be sure - Blizzard can be misleading (and usually is...)
Full Resolution Version
Runes

The rune is
Aegishjalmur. It's a viking rune for protection and irresistibility in battle. Probably Blizzard pointing to the Lost Viking series. Also, as fans speculated before, the runes form a pentagram:

The Puzzle is Complete
While only one picture of ""Mr. Purple"" was added to the CSS file, fans found the last piece as well (a mistake by Blizzard? The next hours will tell).
First image

""Harbinger""? Harbinger of Destruction (AKA Diablo). And what about the artist signature? Rabid Diablo fans will probably crack the mystery as the day goes on...
Second image

Final Puzzle

What the hell are we looking at? The bottom of the CSS file implies:
evilpenguin {background: url('/_images/42.jpg') no-repeat 0 0}
What does an evil penguin has to do with... anything? Damn you Blizzard and your mind tricks!
It's now obvious the numbers doesn't translate into the English ABC (42?!) and they are merely the numbers from the Lost TV show (as one theory suggested yesterday).
Stay tuned as we update this entry with more details and speculations as their come.
Meanwhile we wish to good luck to our crew in the air (on their way to Paris):
LordOfAscension,
Dauntless and
ChaosSmurf, who will cover the event tomorrow. You will all be able to watch the WWI, including the opening ceremony and the game announcement through a
live stream set by Blizzard.
Sources:Blizzard.comCSS FileWWI Stream