Ok, maybe not a cult movie, but it is one that, to me is underrated.
Time Trap.
I watched it on Prime on the off chance one evening a couple of years ago. I was hooked. Acting not the best, I think all unknowns, but adequate. The plot and general over all theme and idea was really good and the ending made me want more, just like, an extra 10 minutes to expand on the ending really.
really good film, certainly not Oscar worthy, but up there with some great sci-fi movies.
Edit: Ahh. Maybe these two to add. Class of 1984 and Class of 1999.