AVault has posted an interview with David Grenewetzki, president of Sierra On-Line. The interview (which would appear to have been conducted just this afternoon), talks mostly about their "restructuring" announcement, but there's also this bit which appears to confirm that Half-Life 2 is in production (as if there were really any doubts) and even that Homeworld 2 is being considered. Here's an excerpt:

Moving forward, we have Homeworld, which just shipped, and its sequel, Homeworld 2, which we are currently evaluating at this time. Also coming from Valve are Team Fortress 2 as well as Half-Life 2, and Mark’s got an incredible design team in Impressions Games, probably the most successful group within Sierra, which is shipping Pharaoh, an incredible title, this year.