"Nowadays, John does some TV commercial voiceover gigs, and some voice work for Valve that he couldn’t elaborate on" -- anybody hope it's HL3 they're talking about here? :)
In the same way as Link from the Legend of Zelda, I'm kind of glad Gordon doesn't have a voice actor. Too often the disembodied narration in first person games comes off as hammy.
I remember when Ashly Burch said she did some voice acting for Valve. People thought it might be HL3 related, but it turned out to be for a TF2 video. The lesson: Of course Valve is working on something, they're a video game company, but saying a voice actor did some voice acting at a video game company says almost nothing.
Edit: Oh, and she's the Announcer in Team Fortress 2.