Gabe Newell posted in a thread on the HL2 Fallout Forums that the Half-Life2 Release Candidate has been sent to Vivendi for approval. Here is his short but sweet post:

Yes, the RC went to VU yesterday.

So what does this mean? Well, of course Vivendi will very carefully check such a big hit as HL2 and as Gabe mentioned before that can take two weeks or more. If everything goes well we'll have a "gone gold" anouncement in early October. Can't believe it, HL2 will finally be out soon, heureka!