I have personally reviewed the books in this list.
Eddison, Sydney A Passion for Daylilies. New York: HarperCollins Publishers, Inc., 1992. A very readable historical account of the people and organizations behind the development of the modern daylily. May be out of print. If you can find a copy, get it! Otherwise check your local library. A "must read" for all daylily and gardening enthusiasts.
Gatlin, Frances Daylilies---A Fifty-Year Affair. Edgerton, Missouri: The American Hemerocallis Society, Inc., 1995. A history of the American Hemerocallis Society, with many photographs, including all Stout Silver Medal Winners. Check with the AHS to see if they are still available.
Gregory, Ken and Kay Eureka Daylily 1998 Reference Guide. Granite Falls, North Carolina: Ken and Kay Gregory, Vol. 8, 1998. Published annually. A reference of currently available daylilies, with registration data, sources and prices. Award winners listed. Articles on daylily personalities, many color photographs. Every daylily enthusiast should have a copy. See the Eureka! Web site at http://www.GardenEureka.com.
Grenfell, Diana The Gardener's Guide to Growing Daylilies. David & Charles Publishers, Newton Abbot, Devon UK. and Timber Press, Portland, Oregon, USA, 1998. This is a complete reference book about daylilies, and it also makes enjoyable reading. Descriptions of daylily culture in Europe, North America, Australia and New Zealand give this book global appeal. The latest trends in daylily breeding are discussed. A large section is devoted to descriptions of the best of many popular daylilies, both old and new, and there are a generous number of photographs throughout the book.
Grosvenor, Graeme Daylillies for the Garden. Portland, Oregon: Timber Press 1999. This is a basic guide to daylilies and how to grow them. There are tips on photographing daylilies, and even a section on the culinary aspects. The book contains many photographs of daylilies introduced in the 1990's, and a descriptive listing of the author's recommended cultivars.
Hill, Lewis and Nancy Daylilies: The Perfect Perennial Pownal, Vermont: Garden Way Publishing, 1991. A practical guide to growing daylilies. Many color photographs.
Munson, R.W., Jr. Hemerocallis, The Daylily. Portland, Oregon: Timber Press, 1989. This book, by the master of the tetraploid daylily, is likely to make a daylily enthusiast out of you. Has sections on species daylilies and the hybridizers. Its most outstanding feature is a descriptive listing of what Mr. Munson considers to be the most outstanding daylilies. Most of the daylilies listed were registered in the 1980's. Many color photographs. A classic.
Petit, Ted L. and Peat, John P. The Color Encyclopedia of Daylilies. Portland, Oregon: Timber Press, 2000. The very readable introductory chapters on the daylily plant, on species daylilies and on the history of daylily hybridizing set the tone for the remainder of the work. Rather than attempting to out-do the many previously published works covering the subjects, the chapters summarize the the material. The remainder of the work is an incredible listing of photographs and descriptions of the most popular daylily cultivars at the end of the twentieth century. Rounding out the work are chapters on hybridizing and daylily culture, followed by a collection of unregistered seedlings by many hybridizers. By now, you probably know many of the seedlings by a registered name, and are growing a few in your own gardens.
Track, Norman S. Daylilies. Toronto, ON: HAWKEYE, 1997. An illustrated book for enjoyment and reflection on the wonders of the daylily.
--- Daylilies: The Beginner's Handbook. Edited by Frances L. Gatlin. Jackson, Mississippi: The American Hemerocallis Society, Inc., Revised Edition 1991. All you wanted to know about daylilies and how to grow them
--- Daylily Encyclopedia. Edited by Steve Webber. Damascus, Maryland: Webber Gardens, 1988. A listing of some favorite older daylilies.
--- An Illustrated Guide to Daylilies. Edited by Frances L. Gatlin. Kansas City, Missouri: The American Hemerocallis Society, Inc., Second Revised Edition 1999. All you wanted to know about daylilies and how to grow them. Updated material on foliage habit, plant markers and daylily forms including Unusual Forms and Polytepals. Many new color photos. If you have only one daylily book, this should be the one.
--- The New Daylily Handbook for 2002. Edited by Frances L. Gatlin and James R. Brennan: The American Hemerocallis Society, Inc., revised 2002. Review pending.