What are the best GOG titles that are NOT on Steam?

rollercoaster tycoon

Neverwinter Nights 1

Tyrian 2000

Nox and NFH + Carmageddon .I just like this games sadly I didnt buy NFH because was saving money for SSS . And almost forgot one nice RTS Tzar

I loved startopia.

Dungeon Keeper 2, Blood, Syndicate

Guilty Gear series.

Wing Commander series

Silver

Theme Hospital and the Dungeon Keeper-series. You won't be disappointed!

Total Annihilation Series and Star Control Series are 2 that come to mind for me

Planescape:Torment, Baldurs Gate:SoA/ToB, NWN 1, Arcanum.
PS System Shock 2, maybe.

MAster of Orion 1

Cannon Fodder obviously..:D

Let's see; I don't think any of these are on steam.

Dungeon Keeper, Blood, Redneck Rampage, Might and Magic series, Ultima series, Shogo, XIII, Clive Barker's Undying

Populous 3 and Blade the edges of darkness (best sword combat gameplay ever in a videogame)

Zeus + Poseidon

Caesar 3

Pharaoh + Cleopatra

Moto Racer 2.

Here's what's on my wishlist over there:
Journeyman Project 2 -- never played 2 or 3, just the first one -- unfortunately GOG doesn't have the first one
Total Annihilation -- awesome RTS, one of my all-time favorite games
Sanitarium -- I've only ever played the demo and keep hearing good things about it :(
Zork: Grand Inquisitor -- I liked Zork: Nemesis a lot ( my first Zork, and yes, I know it's way different than the others), and Z:GI has Tim Curry (I've never played it)

Edit: Just saw your wishlist image. Haven't played much of any of the older D&D RPGs, but I mean to one of these days. They aren't on my wishlist since I do own them through another site. Also, I wouldn't be surprised to see them on Steam eventually -- I believe they have database entries already, but that doesn't mean they'll definitely arrive. Good call on RCT! :) I own that one on disc already. (TA is on my wishlist despite already owning it on disc because it's just that awesome.)

Privateer, Imperium Galactica

Well, I found Simon the Sorcerer 1 & 2 to be great adventure games. I'm actually waiting for a discount on GOG to get them...

Master of Magic

Heroes of Might and Magic 3 Complete

• Sid Meier's Alpha Centauri
• Anachronox
• Giants: Citizen Kabuto
• Baldur's Gate Series* (I, II)
• The Ultima Series (I-III, IV-VI, VII)

And I prefer GoG to Steam anyway. No DRM, tons of extras, simpler installation, better corporate culture**.

*While Baldur's Gate EE is on Steam, what I heard is that it's a buggy mess with weak extra content. It's still better to mod the original version.
*CDProjekt goes well out of their way to satisfy their customers, whether it be removing DRM from -all- versions of Witcher 2 just after release, replacing broken Collectors Edition items (I now have two* Geralt busts because of this), ensuring that old titles work on modern systems smoothly, providing in-depth modding articles, etc. Compare this to hats, trading cards, and the community market. See what I mean?

-Edit-
Outcast and Septerra Core may be worth checking out as well.

Krush, Kill & Destroy series, Heroes Chronicles: All chapters, Nox, Sanitarium, Disciples: Sacred Lands Gold, Betrayal at Krondor series and many, many others. And lots of are still missing on both platforms.

What's GOG?