Aside from the fact that for obvious reasons, Nintendo on any non-Nintendo platform wouldn't happen, no NES amongst the choices alongside the SNES and N64? I am disappoint.
From those listed, I would go with Arcade, Amiga and Commodore 64. The MSX would also be appreciated if at all possible.
As an aside, would you be willing to do any translation work for any Japanese games on Japan-based platforms, if they were to reach GOG, if possible? Monster World IV for Genesis/MD is one such example.
Crom84: I really have no desire to play console games on my PC.
There are so many good old games for the PC that I would love to play again or discover for the first time. I thought the whole point with GOG.com was to make good old PC games available and playable on Win XP / Vista / 7 systems.
I think that it would be a bad thing if GOG suddenly started using their resources getting console games working on the PC instead of making PC games work on newer systems.
A NES game will always work in a NES console and either are not hard to get, but old PC games can be hard to get a hold of and almost impossible to get running on newer systems. That's why GOG is so important to me and the PC gamers around the world. You are not only making the games available, you are making them playable.
Most people own a Nintendo Wii and have through the "Virtual Console" shop already access to tons of old console games (even C64 games). The Xbox 360, PS3 and PSP have got a similar service, but none of them got any old PC games.
This also means that there's no chance in hell that Nintendo or Sony will allow their old games to be ported and emulated to run on the PC.
So please GOG, stick with PC games.
The PC gaming community really needs it.
The thing is, the console makers pay little mind to the retro console side, including Nintendo, who have gone weeks without adding a single game to VC. And there are only a handful of C64 games on the VC here in the US. Besides, the more avenues for old, and also previously unreleased in the US/Europe/etc. games on which to appear, the better. Besides, there's something to be said for the convenience of being able to play from your desktop.
And regarding the NES, good luck playing games with the standard front-loader. (I exaggerate a bit, but still.)