Ok, take this next bit with a grain of salt, but you can head over to www.black-aperture.com for what looks to be an official site for Half-Life 3. It goes without saying that this could be a complete hoax, but it's one of the best looking ones we've seen in a while. And let's not forget about Newell saying that E3 will see an announcement with "3" in it's title, which limits the announcement to just about everything in Valve's catalog.
The site title comes up as Status: Mark 7, and clicking the Half-Life 3 logo [which appears the same as everything we've seen so far] brings us to the page for the Orange Box. We'll have to see how this all turns out, because it all looks a bit too good for Valve not to say anything about it.
However, that Gabe Newell has proven time and time again to be a crafty sonofabitch.