I just got my copy of Tom Richmond's The Mad Art of Caricature: A Serious Guide to Drawing Funny Faces in the mail. As Tom Racine so wisely put it, "It does for cartoonists what [Tracy Hickman's] X-Treme Dungeon Mastery does for Dungeon Masters."
One 30-minute pass through the book tells me that this is going to be my go-to reference work for cartoon faces for years to come. One page in particular, describing something I do poorly, said (and I paraphrase) "this is difficult to do correctly. Here is how to solve that problem." So basically the book paid for itself with just one page of its 170-plus pages.
I haven't learned as much in a speed-read since I skimmed Andrew Loomis' Figure Drawing for All It's Worth. That book and this one will now share a shelf next to my drawing table.