hi mo,

the all-time begonia bible is by Mildred Thompson. it's simply titled "Begonias." it's fabulous, explains each begonia grouping clearly, contains tons of culture info and a healthy amount of pictures...the downside is that it's out of print so you'll have to scour ebay or used book stores. it's a matter of luck to get one inexpensively...i paid around fifty for mine, but i've seen it go anywhere from $20-150.
if you're interested in taxonomy and natural history, there is a relatively new book out by mark tebbitt, also entitled "begonias." those are my two faves. there are also some older volumes that might be great for care info. one that i can think of is All About Begonias by bernice brilmeyer, which i usually see listed for less than five bucks.

hope that helps!
-ming

Thanks Ming! I'll look around.

-Mo

One you're more likely to find at a library, or through an inter-library loan program (or inexpensively used) is

Begonias - indoors & out
by Jack Kramer

its written on a more basic level, and while the infomation is good, its very straight forward.

Its a little old-timey, and the hybrids it mentions are difficult to find nowadays, but its got some really good basic information.

Also, check out the ABS (American Begonia Society) webiste - they have a series of articles that are available to the public. Its grouped by Category - Rhizomatous, Cane, Tuberous, Shrub-type, etc.

Best of Luck!
-Jane

PS - the Thompson book is THE book to get. I lucked out and got a good used copy at a silent auction for $50, which I thought was a real bargain!