Here are my types:
Baldur's Gate 1, 2
Planescape Torment (almost impossible, no one knows who has the rights to it)
Icewind Dale 1, 2
Interstate '76
Arcanum
Homeworld 1, Homeworld Catalysm
Jagged Alliance 1, 2
G-Police
The Legacy of Kain series
Rogue Squadron
That's all for now. :)

ultima underworld 1+2 and all the ultima games (old ones in a collection maybe??) - all difficult to get working on modern PCs

As long as i get C&C-franchise I'm happy. :)

The Battle Isle series (Blue Byte, belongs to Ubisoft nowadays)

Almost forgot
Psycho pinball

Planescape:Torment
Baldur's Gate/Icewind Dale Series
Arcanum (although my old disk still works on my current computer)
Blood 1 (the sequel wasn't very good)
Bring these, and I guarantee I will buy them. =)

Harvester
Loom
Normality
Arcanum
The Dagger of Amon Ra
The Colonel's Bequest
System Shock 1 & 2
I have no mouth and i must scream

It's already been said, but:
Return to Zork
Zork: Grand Inquisitor
Zork Nemesis: The Forbidden Lands
Zork: The Undiscovered Underground

Fighting Steel by SSI (well, all games by SSI :)

I'm writing down my own list, in order of importance.
I'll try to keep it updated.
1. Planescape:Torment
2. Gorky 17 (aka Odium)
3. The original Bard's Tale trilogy
4. Ultima VII
5. Deus Ex
6. Ultima Underworld
7. Outcast
8. Prisoner of Ice
9. Shadow of the Comet
10. Shadow Caster

Baldur's Gate series + Expansions for each.
Icewind Dale series + Expansion + Trials of the Luremaster
Planescape:Torment
Hmmmm... Psychonauts, maybe?
Oh, what about the Masters of Orion games as well?

Here is my current wish list.
Links lead to http://www.mobygames.com
1. Master of Magic
2. Alpha Centauri and Alien Crossfire
3. Arcanum: Of Steamworks & Magick Obscura
4. System Shock and System Shock 2
5. Deus Ex
I just wish one of the attempts at a sequel for Master of Magic had been successful, it's probably one of my all time favourite games.

1. Archimedian Dynasty
2. Grand Prix Legends
3. Death Rally

Majesty plus Expansion
Master of Orion series
Star Control series
Of those, I would want Majesty first, please! My roomies and I had too much fun with that game. I always wanted a true sequel.