Thanks for the tip, it's added now: http://www.imcdb.org/movie_165361-Highway.html

Nice! I think you nailed it. I really had no idea what it was. Thanks!

Blarf, I was way off, it's a '70-'72 Monte Carlo. The side markers are hidden in the trim.
If you remember the front end; an eggcrate grill means it's a '72, I can't find any external differentiation between '70 and '71.

There are of course many more shots of the vehicle, I just chose this because he cuts off the roof with the saw. Since it used to be a hardtop it's especially difficult to figure out.

Earlier then '68, since it has no side markers.
...
That's all I got.

Does anybody know what kind of car this is?? Any guesses at least?

This is from the movie Highway with Jared Leto and Jake Gyllenhaal:

http://www.imdb.com/title/tt0165361/

I was going to make a page for it but I accidentally returned it. There aren't that many notable vehicles in the film, only this hardtop turned into a convertible. The two main characters go on a road trip with a girl that they meet. The girl (Selma Blair) tells them they are doing it the wrong way by not having a convertible. So Jared Leto takes a rotating saw and cuts the top of the frame off while Jake Gyllenhaal is still sitting in the driver's seat asleep! John C. McGinley (Scrubs) also plays a hilarious role. I would recommend this movie if anyone wants to make a page for it, I'll probably make one someday...