Okay, I've updated the list.
Raven's games have been published both by iD and Activison, so I'm gonna go ahead and guess that Raven themselves has the rights.

I'm not sure how reliable this is, but according to Wikipedia: "Raven made an exclusive publishing deal with Activision and was subsequently acquired by them."

That's good enough for me... I'm adding them now.

Homeworld games left for THQ with Relic. You won't be seeing the Mechwarrior games either, although I think that Activision has about as much right to them as is possible (they inherently use stolen content).

id was bought by Bethesda recently.

Nothing that's not third hand info, I'm afraid. From what I gather some of the mech designs too closely emulated others owned by another company. A trend which has continued with the latest Mechwarrior it seems.

Heh, I've never been into mecha, they pretty much all look the same to me anyways... But I guess I shouldn't brag about ignorance...
Never really heard about the games until now. Are they any good?

Thanks OP, great list and I look forward to seeing how many GOG are going to work on.....

Yes, but Activision still published their old games. I'm guessing they don't have the power to put them on Gog though.

So what games do you suppose gog.com will secure the rights to selling? Personally I'm expecting most games from them most wanted list, maybe except for Hellfire and the MechWarrior games. Bloodlines I'm not sure about since it's kindda new and might require some sort of DRM.
I'm guessing we're going to see a Leisure Suit Larry collection, hopefully it will be the "Ultimate Pleasure Pack" which includes game number 7.
Hexen/Heretic should be an obvious choice.
I'm also expecting some games by Impressions Games (Caesar 1-3, Pharaoh and Zeus), since they're famous for making good games and bad advertisement. Kindda like with Psychonauts and Grim Fandango, except even more obscure.
And of course there should be a Zork/Infocom collection of some sort.
And I'm hoping to see Lawnmover Racing Mania 2007... Just because I'm unable to take that title seriously in any way.
Who makes a game like that?

Hopefully as many of the old Sierra titles as possible. Larry, King's Quest, Police Quest, Quest for Glory, Space Quest collections.
NOLF1+2. Older Sierra adventure games also, like Robin Hood: Conquest of the Longbow, or the Laura Bow games.
GABRIEL KNIGHT 2 + 3.
PHANTASMAGORIA 1 + 2.
I'm not that hyped about ID (won't happen) or Blizzard (won't happen) games, as those developers still hold the majority of the say and sway over where and how their games are published. Specifically, ID is only on Steam aside from their own store, and Blizzard is only on, well, Blizzard.
But old Sierra stuff - hoo yeah. Bring it on.

It's weird how many votes Phantasmagoria has received, even though the reviews of it aren't exactly fantastic...

None of the Phantasmagoria games are that fantastic gameplay or storywise, but ... cult classic FMV game.
I can't help it, I'm a sucker for those old FMV games. Brings me back somehow.

List updated. So what do you guys suppose is next? Kings Quest? Gabriel Knight 2? No One Lives Forever? Bloodlines?
Also, I've removed the MechWarrior games...