AMC Pacer X
Ford Gymkhana 9 Focus RS RX
Lola
Mazda Rx-7
Mercedes 300 SEL 6.3
Nissan Silvia K's
Porsche 356A
2004 Porsche 911 GT3
1970 Porsche 914/6
Porsche 928 GTS
Porsche Cayenne Turbo
Porsche Cayman GTS
Porsche Macan Turbo
Ram Runner Horizon Edition
These are the rare ones. I would say the rarest and most expensive is the RAM Runner HE.
I think the biggest hype is about the Silvia nowadays, I have lost 3 Silvias, one as a buyer, and two as a seller. But in the meantime more and more Silvias started to show up in auction groups, so it's not that hard to find one.
But the new Forzathon list is in the air, and if it's real, then the Cayenne and Cayman GTS won't be rare for a long time, better to start sell them, because at the moment they have a value.