I am still waiting for a 1st-gen Peugeot 106 Rallye similar to the one that my father has:
http://antp.be/pic/mp_peugeot106.jpg
We already have a 2nd-gen one:
http://www.imcdb.org/vehicle_720-Peugeot-106-Rallye-S2-1996.html
(but only one)
It is quite rare, especially the 1st gen: they made between 3000 and 5000, and not so many of these were used on road.

A Mega Track would be nice too
http://fr.wikipedia.org/wiki/Mega_Track
(sorry there is no English version of the page)
It is a very big and very expensive off-road sports car (!)

A 2nd-gen Maserati Quattroporte.
http://en.wikipedia.org/wiki/Image:1974_4porte_800x600_1_G.jpg
We already have only one 4th-gen (+ a drawing) which is not so rare, I do not know when we will get a pic of one of the thirteen 2nd-gen which were made.

I'd also like to find in a movie a US-specs Citroën XM (which would actually be a CXA XM), as they are quite rare.
http://forum.imcdb.org/forum_topic-155-11063-French_cars_in_the_USA__Voitures_francaises_aux_tats_Unis.html#p11063

A good pic of a Talbo Tagora could be nice, as the three that we have are barely visible.
http://www.imcdb.org/vehicles.php?make=talbot&model=tagora