Timothy,

I posed a similar question about doll identifications just a couple
of months ago.  There are a variety of excellent sources, especially
if the specimen includes a maker's mark.  Regardless, though, an
excellent book is  The Collectors Encyclopedia of Dolls, by
Dorothy S., Eliazbeth A., and Evelyn J., Coleman.  They have many
great photos of china heads and descriptions.

Brian Siegel