I sincerely believe
that HL3 is going to be officially announced within a month. I have no real evidence, just wild conjecture and ♥♥♥♥♥♥♥♥, but HL2 came out on Nov. 16, 2004. I think Valve can get HL3 finished by that date next year for a 10th anniversary spectacular. Which means they could fairly announce it on Nov. 16 of this year.
Or, if Gabe Newell really wants to bury those demons he brought on himself with announcing HL2 before it was ready, he could announce HL3 on the same date next year, March 21, on which he announced HL2 back in 2003. If he went this route, he might have HL3 ready to ship on Sept. 30 just to prove that Valve can make a deadline.
This is fun with numerology, of course. Any thoughts?