Sorry to be the mature one here. But I doubt you are going to get any DOS games being sold here, because I cannot see how they could guarantee they would work unless they did a deal with DOSBox (a utility that allows you to easily play DOS games in an emulator). It may be difficult legally to charge for a game that only runs because it has a freeware utility included that runs it.
You have to be a clever consumer though, as some of the games mentioned are now freeware, or there is no way to know now who owns the copyright and therefore are considered 'legal abandonware'.
The problem with who has the legal copyright for these old DOS games would make it impossible for G.O.G. to be even able to approach anyone to get permission to sell.
Also, to the person who said they could host free games, well, there are plenty of other sites that do that,, and this is a business. it is no different than Steam, and no one would expect steam to carry free games. In fact, Steam doesn't really do much to any games they sell to make them compatible in the way G.O.G. does. I know of people that bought retro games from Steam and found they couldn't patch them or add mods, etc.
So when listing games you;d like to see,. remember they need to be at least of the win95/98 era (1996+), so the request for the X-Com games are no go (Steam has them), System Shock 1 and 2 is unlikely because the first one is DOS and the second does not have an obvious copyright owner for GOG to approach.
Same goes for the Ultima series and the LucasArts titles, etc. All DOS games.
I would suggest for DOS games you buy via ebay and download DOSBox with one of the user friendly front ends like the D.O.G. front end and get them working on your XP/Vista machine that way. Once you get the handle on DOSBox/D.O.G running these DOS games is quite easy.
As to games like Jagged Alliance (the first one) and the later Gabriel Knight games and the Baldur's Gate/NOX/Icewind Dale/Neverwinter Nights RPG's and other games of that era and later I say 'bring them on....!!!'
Wasn't Descent 1 a DOS game? I'm not completely sure, but that would give us hope GOG can also offer us DOS games ;)
Also, while I see your point, I think it is important that we also suggest those titles. The whole point of this or similar threads is that the folks at GOG know what games their users want, so they can put effort into getting them into their catalogue. Even if DOS are harder to offer or if the copyright situation is complicated - if they see that there's a high demand for certain games, this would indicate to the team that it might be worth the trouble to bother with copyright situations or, if necessary, do a deal with the DOSbox team or whatever.
Also, the concept behind GOG is to make the games compatible with XP and Vista. I'm not exactly sure if there's much difference between old Windows games that don't run on modern systems and old DOS games that don't run on modern systems. They have to work on the game either way, and since compatibility is one of their main advertising arguments, I wouldn't be surprised if they had a way to handle DOS games without using external software.
I know a lot of games are available as abandonware and that it isn't too hard to get these games to run with DOSbox. I just recently started playing Albion again. Still, it would be nice to have a version of the game that doesn't require additional software to run, simply because it would be far more comfortable.