Update: Blizzard's VP of Game Development,
Rob Pardo, was the keynote speaker at the
Game Developers Conference in Paris that just wrapped up a few days ago. During a Q&A after his speech Pardo was asked to comment on the new game rumors, specifically those pertaining to Diablo III being announced at this years WWI. His answer will only fuel the speculation:
So you want me to announce the game before our announcement?"" he said. ""No offense, but I think there's like 300 people here, and I'll be ripped apart by 8000 people there [at the Invitational] if I pre-announce it - but it's going to be really exciting. I think everybody here will be really excited about the announcement.
Source:GameIndustry.biz - Pardo Fuels Flames
On the third day since the splash screen first appeared on Blizzards sites, most of the community is now quite confused. While SC:L will still offer officially: No Comment, we'll continue to keep you updated on what the community is thinking.

New today:
The third splash screen - About to crack open
The third rune - A Protoss logo
The third puzzle piece of the purple monster - The upper right corner (23.jpg)
And lastly the third name that came along with the puzzle piece. - icy
The new rune is in fact the
StarCraft II Protoss logo.

So it seems like the first rune is from the Frostmourne and
World of WarCraft: Wrath of the Lich King, the second a Hel rune from
Diablo, and the last from Protoss in
StarCraft II.

The puzzle piece of today is named
23.jpg. The name that came along with the puzzle piece was ""
Icy"", which may refeer to the Diablo II area
Icy Cellar. Note that all 3 keywords are pieces of names from the fifth Act in Diablo II. Respectively,
The Frozen Tundra,
The Drifter Cavern and
The Icy Cellar.

23 being letter ""
W"" in the alphabet.
So far the letters we got chronologically make out
D O W. We can however put the pieces together like this:

As many predicted, what seemed evident yesterday, is clouded today.
Sources:BlizzardBlizzard CSS File