The inexpensive answer is use a Canon FD body like an AE-1 program or a FT QL/FTb specifically for portraits. No AF, but you can use either a FD 135 2.5 lens on it ($60 for the lens) or a really, really good FD 85 1.8 ($200). Trust me, I tried every Nikon lens from 85 to 105 known to man and none of them were as good as these Canons, which are pretty close to the Leica R.
Momus,
You should not write these kind of posts or you'll drive the Canon FD lens prices up. Greeting from a Canon FD/FL/R fan which of course owns the 135/2.5.
Now, to be honest, I can recommend some lenses on the Nikon system that are, in terms of image smoothness/bokeh/portrait quality, as good as any Canon counterpart, so the OP can stay within the Nikon system, an excellent brand with so many great camera bodies. Besides the 105/2.5, which has a deserved reputation, i would suggest:
- The pre-AI 50/2.0 lens. Here Nikon > Canon at least in doing a 50mm lens that is )1) sharp, (2) small and and (3) with great bokeh. The Canon FD/FL system's standard lenses give you only 2 of these 3 qualities at a given lens.
- The pre-AI 135/3.5 is just great, and I prefer the 135mm length for portraits, after having spend good money on a Canon EF 85/1.8 (which is as close to a PERFECT lens can be), and a Canon FD 100/2.8. Those two are perfect lenses but at the end i find the 135mm focal length better than the 85 and 135 for portraits, once you can get enough physical space to be able to use it.
- The pre-AI 200/4.0 has amazing bokeh. I now own the 200/4.0 AI version which is damn sharp, but it is a bit more expensive.
There is a fourth Nikon lens that is the Nikkor manual standard lens with the best bokeh ever, but I will not mention which lens it is, because I don't want prices to go up.