Outcast! That license should be cheap by now, right? It needs to be revived...
Also, Beyond Good & Evil would be awesome. With the sequel finally announced, it would also get a lot of free publicity.
Getting more realistic, maybe Tomb Raider 2? There is a leaked version for the Zodiac that works quite well. Might be possible to get a deal like Tapwave obviously had and maybe build on the work already done? No idea who did that port, though...
Indie games have already been mentioned. They are probably the most attractive games to get ported. Reasons:
-Most are not on handhelds, so a Pandora version would be handheld-exclusive.
-They get a lot of attention lately.
-They are often simple enough to run well on the Pandora.
-Their developers actually deserve the money we throw at them...
If we can establish the Pandora as the handheld for indie games, I think we are in for a big time win.
Some specific titles and developers:
-World of Goo: Sounds like it wouldn't be that difficult to get, main obstacle might be performance.
-Introversion games: They seem to be under some financial pressure so they might be open for a deal. On the other hand, they are very busy for the same reason. IIRC there is a source code CD of Uplink for sale. Not sure a port could be made with just that but it certainly makes it seem like the possibility is real.
-Crayon Physics Deluxe: Could be great with the touchscreen. There is the open source clone Numpty Physics but from what I can tell the original is better and could sell some Pandoras.
-Aquaria: Would be awesome...
-Gish, Super Meat Boy etc.: Sounds like Edmund McMillen would be very open to a deal!
-Fez: It's not even out yet but it looks very awesome. Could be very good publicity if the Pandora would be it's launch platform...
-Cave Story: There have been free Cave Story ports to handhelds before but now there is a commercial version coming to WiiWare. Getting a handheld port of that would be great.
What I don't think we should waste money on is big names with low budgets. Tapwave had some of those and they were pretty much crap.
A great source to get good commercial games from are the old PDA developers that are looking for a new home and are mostly moving to the iPhone. Those games do not come with free publicity like a PC indie title, though... Still, Warfare Inc., Bike or Die, The Quest, Mazera, those are some amazing titles.