I'll give another vote for the 105 f2.5 AIS. I've done a lot of portrait work with that lens and it never lets me down. It seems like the perfect focal length for closer portrait work.
To comment on the above post by gnashings: I agree that you can do quite a lot with a good 50mm lens as far as portraits are concerned. It may distort the face a little bit, but in the case of low light situations, it is invaluable (especially since you have a 50mm f1.2).
I think we have similar styles and I feel you're going in the right direction equipment-wise.