As measured by the number of citations in scientific journals, who
were the most important psychologists and psychiatrists of the last
hundred years?  In contrast, who does the educated public believe are
the 10 most important psychologists and psychiatrists of the last
hundred years -- or, indeed, all of human history?

Here are my top nine;

Wundt
James
Skinner
Watson
Freud
Hebb
Lashley
Thorndike
Titchener

I have a bias to more biological psychologists.

I think you'll need to pay at some point, but this might help -
http://www.apa.org/monitor/julaug02/studyranks.html

This link looked intersting, but it wasn't working when I tried it!
http://www.clt.astate.edu/stevenh/ms.htm

Ian G.

I think pforcelli got it right.  The only names I would add for
further consideration, not necessarily due to their genius, but
because of the sheer number of times they get mentioned would be
Pavlov, Jung, and Maslow...

-Rob