I've already voted for all of these:

(For my husband and son)
Earthsiege and Earthsiege 2
Doom series
Nerf Arenablast
Wolfenstein
Commander Keen
Midtown Madness

~ PUZZLERS ~

Shadowgate (any, but especially the re-imagined one)

Civilization 1 & 2

Pandora's Box (GOTY)

Tetris (some of the variations on the original were fun too)

Lemmings, Oh No More Lemmings, and Lemmings 2 The Tribes

original Humans (puzzle game)

Everett Kaser's collection of logic games

~ ADVENTURE GAMES ~

Eric the Unready (and its sequel - if it was ever made)

Freddy Pharkas & Laura Bow (old Sierra adventures)

Starship Titanic

LucasArts Adventures: original Monkey Island series, Grim Fandango, Loom, Maniac Mansion, original Sam & Max, Day of the Tentacle, Zak McKracken etc...

Discworld 1, Discworld 2, Discworld Noir

Sherlock Holmes series (adventure games)

Agatha Christie mysteries (adventure games & HOGs)

Riddle of Master Lu (I've bought mine 2ndhand and have never gotten it to work, but it sounded fascinating!)

Other older adventures like Celtica, Riddle of the Sphinx, Omega Stone, Rhem series, Crystal Key 1 + 2, Timelapse, Cameron Files, Toonstruck, Neverhood, Schizm, Reah, Lighthouse, Morpheus, AGON, Ankh 1, Bad Mojo, Weekend in Capri & Anacapri, Alida, and Tony Tough (gross but funny)

GoG has the Zork series, Feeble Files, Simon the Sorcerer, Gabriel Knight, and some of Myst, Tex Murphy, Darkfall (Boakes was the break-out Indy guy), Sierra's KIng's Quest/Space Quest etc, and some other 'must haves' for adventure game fans, but there are a lot more worth playing. Once people find out they like an adventure game like Myst, and that there are relatively few available now, they look for these titles 2ndhand due to recommendations, so if GoG can get them cheap, it should be a moneymaker for them. I'd be happy to repurchase many of these to run on modern machines, as my finances allow.

Excellent edutainment 'adventures'
Macaulay's How Things Work 2.0 & Pinball Science
Bioscopia, Physica, Chemicus
Dr Brain games
Humongous kids' games: Freddy Fish, Spy Fox, Putt Putt (I don't need them for myself, but it would be nice if they were available to today's families)

The classics from from old Infocom that aren't Zork. I love Zork, but they released other classics too: esp: Trinity, Bureaucracy, , Hitchiker's Guide to the Galaxy, [url=http://infocom.elsewhere.org/gallery/nordbert/nordbert.html]Nord & Bert Couldnt Make Head or Tail of It, Hollywood Hijinx etc
see http://en.wikipedia.org/wiki/Classic_Text_Adventure_Masterpieces_of_Infocom or http://infocom.elsewhere.org/gallery/greybox.html
(I personally have a number of them onstore-bought cds from the 90's, but would love to know a forward compatible version was available)

~ Assorted ~

Chronotrigger, FF VI & VII, Mario rpgs
(Yes, I know, these aren't at all likely, but you asked)

more Adventure, Puzzle. & Hidden Object Games generally...

Silent hill 2 was, and is much better than 3 or 4.

DRM Free Kristen Bell

The Amiga version of Neuromancer. (One can dream.)
Not the PC version, it was released when graphic and sound sucked on the PC, the C-64 version was way better.

All Infocom text adventures in one package.

Harpoon

A good Chess game. (In fact more board games)

Gunship 2000
Jane's AH64D Longbow
... All Apache simulators

Aces over the Pacific
Aces over Europe
Aces of the deep.

Chuck Yeager's Air Combat.

The Steel Panthers series

I was a Strike Fleet guy myself (http://en.wikipedia.org/wiki/Strike_Fleet), but really any surface naval sim would be awesome.

(Voted for Harpoon.)

Someone just PMed about this game and there's an online paper trial of me trying to get it to work about four years back:

Starfighter 3000 (3DO)

Windows 8 support for Conquest: Frontier Wars

Arcturus I had previously only voted for games I "REALLLLLLY" wanted but you post has inspired me to vote for a very good game and one I always wanted but didn't pick up back when...

Wish listing Uprising 1/2 and FAKK

AoE Games
Star Wars games
Majesty series
Civ games
Close Combat: A Bridge Too Far
Team Xtreme: Operation Weather Disaster
Escape Velocity Franchise
The Learning Company Games (Math Mountain)

*Edit* AND SIM FARM AND SIM ANT!!!!

Ooooh thanks for the reminder I would LOVE to play CC A Bridge Too Far again. I know I'm shirking my grognard roots but some of these hybrid RTS/TBS games were pretty damn good (see the recent love for Gettysburg! here!)

KOTR KOTR!! ( I know its a pipe dream)
The older star wars titles, like Tie Fighter, Jedi Knight games
Lucasfilm games, Grim Fandango, Zak Macraken, Maniac Mansion
Infocom games, love infocom!
The first AVP game
System Shock 1
Neuromancer
The AD&D Games, like Pool of Radiance
Vampire Masquerade
The Last Ninja
The Bards Tale 1, 2, 3

I know there is more, this is all I can think of atm tho.

Maybe in your next life :P

Hey, get out of my head!

Not a lot of classics I am still drooling for other than the obvious Lucasarts and Bethesda stuff, honestly. I'd like to see more newer games here in complete editions, like say the Mass Effect trilogy or Assassin's Creed 2 and up. Stuff that, now complete, should be made available for archiving, which is how I see GOG if I'm being totally honest.

Grandia II

There are more games (many, MANY more), but Grandia II is what I really want to see on GOG.