D.Keys: Not that I know, but since MGS was released I though it would be possible hehe. Syphon filter was indeed Sony exclusives (PS1, PS2, PSP).
Wish all of them were here too. :)
InSaintMonoxide: There was an actual PC version of MGS back in the day already though. I always have the feeling many companies are too lazy to port old console exclusives to PC, even if all they need to do is run a basic emulator. I definitely would like to see all the old stealth games like Tenchu on here too.
Geez. Tenchu... so much fun playing that game back in the day.
Tenchu 1, 2, 3, Wrath of Heaven, Z...
Shinobido too, for the PS2, really cool.
Jigowatts121: The first Splinter Cell is already on GOG but you will need to use the DgVoodoo wrapper to get the shadows working prroperly. There are additional fixes for widescreen and ps3 textures however I prefer not to use them as I like the game as it was intended. I find these mods lose something...
Pandora Tomorrow isn't anywhere digitally, you will have to find a retail copy and use the aforementioned wrapper and optional widescreen and texture packs.
Chaos Theory is available DRM free but you will need to buy the Ubisoft 25 Years version that has StarForce removed.
Double Agent - I'd gladly never play that game again, it was awful.
Conviction and Blacklist, I can't see being released here any time soon.
Syphon Filter - was indeed a Playstation exclusive so your better off using emulation as thats all GOG would use.
Thanks for the info too!