I'm looking for a definitive list of the top ten book publishers in
the US.  I'd like two lists.  One by $ volume of sales and the other
by number of titles in print.
Please let me know if you need any clarification.

These aren't what you want, but they're close. This page lists
monetary sales for some and company worth for others:
Independent Book Publishers Hall of Fame
http://www.bookmarket.com/fame.html

Other pages on the same site include:

Top Independent Book Publishers
http://www.bookmarket.com/101pub.html

Top Dependent Book Publishers
http://www.bookmarket.com/101pub22.html

Hope this helps.

Even better, from:
Yahoo! Finance
http://biz.yahoo.com/ic/35.html

Top Book Publishers by Sales:

1.  The McGraw-Hill Companies, Inc. (MHP)  
2.  Random House  
3.  Harcourt General, Inc.  
4.  Verlagsgruppe Georg von Holtzbrinck GmbH  
5.  Scholastic Corporation (SCHL)  
6.  Pearson plc (PSO)  
7.  Houghton Mifflin Company  
8.  HarperCollins Publishers Inc.  
9.  John Wiley & Sons, Inc.  
10. Simon & Schuster Inc.  

Google Search Term:
"top book publishers"

hi wassy,

That first site you pointed me to isn't what I specifically asked for
but it looks like a great resource so that's worth at least a buck.

Your second response is exactly what I wanted for the first half of my
two part question.  So you get another buck.

How do I pay you?  I don't see any button anyway on this site for the
questioner to say "Pay the Researcher."

ps.  The last have of my question is still open.  I'm still trying to
find out essentially which US Publisher has the most books in print.

- gagnon

No charge! I'm not an official GA researcher (but not from lack of trying).