A few thoughts:
1.) There are a few indie games on Steam that would be great on a handheld device, even better than on a PC. Two that people have already mentioned are Geometry Wars and Peggle. Also, Lumines would be great of course, but is already so closely associated with PSP that it might not have the same impact.
In other words, games that are considered to be prototypes of their kind. But at the same time, games that are a little older, from smaller developers, currently distributed online (through XBox Live Marketplace or Steam, etc.), frequently already on multiple platforms, lower in price, less complicated (i.e., do not need a full KBM set up or benefit from gaming controls), and with lower system requirements. These games are often known only through being early adopters of online distribution. Not only does that make it seem more likely that a company would be interested in the Pandora, it makes the Pandora better recognized by gamers in general. E.g., Steam is better known than any of the indie games on Steam individually, so by associating the Pandora to one of those games, the Pandora becomes associated with Steam secondarily in the minds of gamers.
Further, a mobile version of a game that has been only available by download on Windows or a major console would be good for everyone. It will make gamers more interested in the Pandora, and for those who do not have a Pandora or will not buy one (i.e., most people), they may be more likely to buy the game on a different platform. Win win.
2) World of Goo would be killer in a lot of ways, because of how successful it has been and because 2D Boy just released that Linux version. If that developer made an exclusive Pandora release, whether an optimized version of the same game, a special portable version, or even a completely different game -- that alone would be news (in the gaming world). It would draw in both Linux and non-Linux users (for better or worse). I think that this might be a little pie-in-the-sky though. If we knew what is going to pop in the indie game market in the next year, that would be ... awesome as well.
3) I think the Pandora could be billed as an ideal micro-environment for game developers interested in entering the portables market.
-a- Easy updating of software versions (compared to cartridges).
-b- A critical and active gaming community.
-c- Limited possibility of piracy into the mainstream portable gaming market.
-d- Any major commercial entity entering Pandora-space would get the immediate and almost full attention of the entire user community.
-e- Street cred.
4) I would love to see Worms (or its online variant that I used to play) or even Diablo. This gets into another issue, and something I have wondered about, which is network gaming, ranging from Mario Kart to TF2. Does network gaming not imply that there will be dedicated servers and increase the investment of the developer? I love online games (Pandora could do voice chat so easily). But there seems to be relatively little going on in the portable gaming market with networking outside of the Nintendo DS, and they have supported local networking since the GBA (?). Like people are saying about some of the older FPS plus online mulitplayer games -- if Pandora could pull off just one of these online multiplayer games well, that would be a handheld gaming milestone, no doubt. (I would want UT2004, in an ideal world.)
Sorry for the long post, I thought I would spit it all out at once.