I'm not sure how obscure films need to be to qualify, but "Lone Star" (
link) should definitely be seen.
It stars Chris Cooper, who is one of my favorite actors, and also features Kris Kristofferson, who is cast perfectly as a scary sonofabitch. At its most basic level, the film is a mystery story, and it is interesting enough on that right. But it also presents a rich portrait of Texas's multicultural history.