Re: I'm touched by the weirdness of this request...
Richard Coyle was an epic Albert Spangler/Moist von Lipwig, however the absolute standout from Going Postal was the inimitable Charles Dance as Vetinari.
I'd always fancied Rincewind as a younger Rhys Ifans; tall, thin, scraggly beard, early 30s in age, slight look of failed academia and desperation, not some bumbling old man who looked like he could barely run 5 metres before collapsing. A Rincewind that cannot run, oh my days...