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My goal in asking this question was to narrow down that long list to:

1) The books people actually *use*
2) Ones that would give me information about what different ingredients do so
I could substitute.  I gave as an example white sauce, and several people
answered that question.  Most said they used corn starch.  Second most popular
was using the usual GF flour mix.  One person mentioned potato starch.

Even though I said I knew about the Hagman books, people still mentioned them,
so they must be good.

Second most frequently mentioned were Carol Fenster's books.  Her "Special
Diet Solutions" engendered a whole gamut of responses - one person was very
negative, one mildly negative, 3 positive.  2 people like her newer book
"Wheat-Free Recipes and Menus", and say that it has tables of what different
ingredients do, and good substitutions - I think this is in both of her books.

The following books were recommended by 1-3 people each:

Fabulous and Flourless" By Mary Wachtel Mauksch (ISBN 0-02-862002-X) (3 people)
Going Against the Grain, by Phyllis Potts.  ISBN 0-9630479-0-6 (2)
Gluten-Free Gems, by Noreen Moses  ISBN 0-9642007-0-8 (1)
"Good Food-Gluten Free"  by Hilda Hill (1)
The Practical Gluten-free Cookbook_, by Arlene Stetzer (1)
AGAINST THE GRAIN by Peters Jax Lowell - this is out of print, btw, at least,
   that's the message I got at amazon.com (1)
Gluten-Free Cookery : The Complete Guide for Gluten-Free or Wheat-Free Diets
   by Peter Thomson (1)
The Complete Food Allergy Cookbook, The Foods You've Always Loved
   Without the Ingredients You Can't Have" (ISBN 0-7615-0051-0)(1)
The All Natural Allergy Cookbook_, by Jeanne Marie Martin(1)
"The Allergy Cookbook" by Ruth R. Shattuck(1)
Wheat-Free World (1)
The Allergy Guide to Brand-name foods and Food additives
   by Stephanie Bernardo Johns(1)
Gluten-Free Anytime and Gluten-Free Special by Joyce Friesan and Donna
   Wall(1)
Great Gluten Free Goodies_  by Rebecca Riley(1)

Also, "regular" cookbooks were mentioned, the Moosewood cookbooks most often.

Thanks again to everyone who took the time to help me out!

Laura