Copyright, trademark, privacy and portfolios

I have been studying privacy, trademark and copyright issues and still don't have a satisfactory answer for this question - I am working on celebrity portraits professionally for book covers, magazines and the like.

Is it permissable to use such a portrait in one's self-promotional literature and on a web site without the permission of the person whose likeness you have used? I am speaking of public figures, politicians, celebrities, etc. I know I can do this legally provided there is permission, or if it is commentary ("editorial exemption"), or under satire, but not for "commercial purposes", but where it comes to adding samples to a portfolio?

Right now I have only samples on my pages that meet criteria I know are legal and ethical, and I want to keep within the law. But that does restrict what I can show, and how I can present it. I have a lot of material I am not showing in my online portfolio because I don't have permissions.

Technically what I am planning on doing is for "commercial purposes" but I am not planning to sell these specific images - only show them as examples of my work. The recent 3 Stooges case has me a little nervous just when I was thinking I'd be okay. I have seen many other artists showing their work online - obviously without permissions. Are they taking a huge risk? What is accepted practice in this regard?