Hmm, I would say Mass Effect 2 because of its DLCs requiring online authorisation. I still believe it will appear here when it's old enough, though.

Luscasfilm Games (Monkey Island, Indiana Jones, Zak McKracken etc)

Dune, good call, I missed that one; especially 'Emperor Battle for', that damn thing is $50 on Amazon. As for Battle for Middle Earth, let me send you mine. I got it in an EA Box Set and I enjoy the games about as much as I enjoy the movies.

Final Fantasy Series

Seconded.

The old SSI Gold box RPGs would be great too.

Dink Smallwood.

Anything with a license which may or may not have run out.

good to see a dink fan around but why ? its free already and runs on anything possible, heck my dink smallwood runs awesome with steam client as well

Why?
I'll tell you why!
Because I'm a freak and for some reason ever since it first came out that name has been stuck in my mind. And it would be funny.

Sim City 2000 is already in the catalogue. I think the odds are rather good that we'll get more Maxis games sooner or later along with some other EA games that are still missing. Heck, I even honestly believe that The Sims Complete has a decent chance to make an appearance on GOG.

Among my "favourite games that will never appear on GOG" are The Punisher and Marvel Ultimate Alliance. The Punisher may be trashy compared to say Max Payne but IMHO it's still an awesome game, especially when you're a fan of the comics and actually play for score (which turns it into a surprisingly tactical experience). Haven't played Marvel Ultimate Alliance myself yet but from what I've heard it's pretty darn awesome. But with Marvel belonging to Disney... who knows. Then again, I still haven't given up on LucasArts games so if GOG manages convince the mouse to release those ones here there might also be a chance for some games based on a Marvel license.

True, but that is a older type game. I'd like to see simcity 3000 unlimited appear. I guess time will tell.

Every game owned by Nintendo, Sony, and their subsidiaries.

Sega I still hold out hope for, though they seem to be very tightly knit with Valve at the moment.

Vampire the Masquerade bloodlines. Area 51, bloodnet, the suffering, Penumbra series, silent hill 1,2,3,4,5

blizzard: diablo 1&2, starcraft, warcraft 1&2
id software: quake 3 arena
microsoft: age of the empires series
valve: half life 1

What's the problem with acquiring this title? Me very sad...