For community software:
You can request a patch from iRex to be able to execute .sh files from the user interface. And Scotty1024 seems to be very active in porting some apps (Sylpheed Claws and a better ipdf, then there is desgin256's GNUChess, for some examples).
And since the whole system is still running as root, you can pretty much do what you want with it. However, one should be careful, because iRex will ask you for a 75 EUR payment to reflash the device, if you make your iLiad unusable.
(someone correct me if I'm wrong in thinking that everything is still running as root)
For packages to port, I would personally be interested in a small webserver (like Lighttpd), PHP5 and SQLite. To bad I'm not a developer.