Hi Peter,
I write birthday cards to my clients but don't send Christmas gifts (there's too many of them)!
I'm doing a Christmas gifts survey on this very topic at
http://tinyurl.com/nbmuva - please take a minute to have your say!
I'm asking what people think of Kris Kringles and how much they'd spend on colleagues and so far, the answer is: not much!
A Christmas card would be fine (if you don't make huge revenue from your clients) but a modest yet thoughtful gift would be a gift card to one of the major online book retailers. Whether they use it for business books or something for the beach, you couldn't really go wrong and you can always discuss the book in your next meeting.
Cheers,
Elizabeth