Those NISA games aren't too hard to find but in a few years they will be because stores don't stock them. I was waiting for Atelier Meruru to go cheap before I got it but its still $67 (NZD) so I might just grab it before it goes up in price.
I have The Orange Box, I got it for $30 and had no idea it was "rare".
Any of the NIS games that aren't Disgaea ones, Rune Factory, Sacred 2, Way of the Samurai 3, Star Ocean: The Last Hope, Trinity: Souls of Zill O'll, Force Unleashed: Ultimate Sith Edition, and Aksys games seem to be rare too.
While I think for most people you wouldn't be able to just walk into a physical store and find those games I think if you into account the Internet I don't see how you can call something rare that can be bought for around $30 with a click of a mouse on Amazon.
To me niche or low sales doesn't exactly mean rare.
PSN ID: sled_dogs76 60" Pioneer Kuro Elite PRO151FD, Yamaha RX-V3900 A/V Receiver, Oppo DV983-H player. Coming soon: 2 Seaton Submersives from Mark Seaton
The only actually rare games I've seen listed here are Uncharted's Collector's Edition, Demon's Souls Collector's Edition and HDN. You can find hundreds of unopened copies of everything else on Amazon fairly cheap. Even HDN is only $60 (HDN mk2 is $80 though).
Playing - Borderlands 2, Hitman Absolution, Vanquish, MGS HD Col, Resonance of Fate, Monster Hunter FU, Demon's Souls, Shadows of the Damned PSN: DocDelicious