When should you contact professors when applying to Ph.D. programs?

I am applying to Ph.D. programs in behavioral sciences (mainly anthropology) in for admission in Fall 2009 (so my application deadlines start December 1, 2008). If I want to contact faculty members that I would be interested in working with, when is the appropriate time to do that? I want them to know me before the application arrives, but not forget me if I contact them too early.

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