A Fiat 500 would be great at least for me, looking at the quality of this model.
It is Italy's most famous car.
I'm biased since my grandfather had one.
There are some free one out there, but most of themare low resolution and not Poser ready as this one.

there is also a tutorial out there to model one, but I've had never the time to develope the required skill to follow it.
http://67.15.36.49/team/Tutorials/fiat500/fiat500.asp

Here are some links with examples:

http://www.500clubitalia.it/index.php
http://nuova500.free.fr/pagine/scheda500l.html
http://digilander.libero.it/Volantino/500/500L.htm
http://digilander.libero.it/Volantino/500/500L_foto.htm

A model of the classic 500 (from version D to R) would be good, my grandfather had a L.