a portraitist who has inspired me quite a bit is the Scot Robin Gillanders, whose book "The Photographic Portrait" was a real eye opener for me in its demonstration that the boundaries for portraiture are very wide indeed. Good blend of formal and more informal portraits, and I can't recommend this book enough. Strangely, Gillanders does not seem to be very well represented on www.
Cate: Thanks for starting this thread. Much needed :-)