I love Shock Corridor. I think it's a great film in every way (just think of that rain scene, check it out if you haven't seen it), not just asylim-wise.
I also think Asylum films would be a fun episode and Shock Corridor has to be better than anything you suggest. Shock Corridor should be in The Canon!
Come at me film-lovin-peeps. I'm one of you and this is my jam. :-)