The best books on Ornamental Grasses, their identification, selection, cultivation and care:

The Color Encyclopedia of Ornamental Grasses, Rick Darke, Timber Press, ISBN 0881924644

The Encyclopedia of Ornamental Grasses, John Greenlee, Rodale, ISBN 0875961002

Where to buy? Local nurseries are always good, because it saves freight.

What part of the country are you in?

Rick Darke's encyclopedia is certainly the best choice if you're interested in a comprehensive treatment of the ornamental grasses that are on the market today. I'd like to have a copy of Greenlee's book because it is often referred to, but it is out of print and I've never been able to obtain a copy (any suggestions?).
However, if you're interested in the different ways in which to use grasses in garden design, "Designing with Plants" by Oudolf and Kingsbury is the book to go for.
To appreciate the beauty of individual grasses, choose either Roger Grounds' "Grasses, choosing and using these ornamental plants in the garden" or Nancy Ondra's "Grasses, versatile partners for uncommon garden design".

dutch...

Abebooks has 70 listings for used copies of the Greenlee book.

I'll cast a vote for Rick Darke's encyclopedia...outstanding pics! Great info!

Greenlee's book is also very nice to have, very informative, and I'd recommend a copy, but was a bit earlier and some changes have taken place (nomenclature and id of certain grasses).