Pentax Takumar 50 f1.4 or Rokinon 85 1.4. You could also look at the Nikon 50 1.4 or Olympus 50 1.4. If you use an FD lens for portrait, I would use a no-glass adapter for best quality (and no need to focus to infinity with a portrait lens).
Thanks, yeah I've ordered a non-glass adapter for this reason
Thanks for all the suggestions chaps... The Rokinon 85mm 1.4 seems to come highly recommended so I'll look out for one of those!