I'd also say "Dino Crisis 2".
Interesting survival horror series, and the odd thing is that I feel it remains pretty strong in the way it was done, despite being the child of "Jurassic Park Mania".
That said, the big PSone games I'd want to actually see on the PSP are actually slated for release, with the exception of "Chrono Cross". There just aren't that many Capcom titles PSone titles that I want to see.
Truthfully I'm looking forward to the release of Dreamcast games more than further PSone ports, either for PSP or full sized consoles. Tech Romancer, Skies Of Arkadia, Armada, and maybe that "horrible" Illbleed game I never played. I think companies should be hurrying it up there rather than focusing on expanding the PSone downloadable library.