A little late responding to this thread, bloom was happening when it started and I'm finally getting time to catch up now that the garden is just about ready for winter.
All the above links are excellent reading material. For those who want a hold in your hands book there are several in my collection that are perfect reading for these long winter days or to give as gifts.
The New Encyclopedia of Daylilies in the link above is simply amazing for the number of images and information. An updated version of the earlier book by Petit and Peat, The Color Encyclopedia of Daylilies, that is also a good read and full of color images.
Another favorite, Hemerocallis The Daylily by R.W. Munson, Jr., has brief histories on some of the early hybridizers and many color images of early cultivars.
AHS Membership makes a great gift (for yourself or someone else!) and includes 4 issues of the AHS Daylily Journal and your regional newsletters.
The AHS has publications too...
The New Daylily Handbook for 2002 is probably my most used book, it has sticky notes stuck throughout marking my favorite sections. I am not certain the AHS has it available any more, but if you can find a used copy ( not mine!) get it!
The new Landscaping With Daylilies book is fabulous and the BEST book available for a real look at daylilies from a garden perspective. Loaded with color images and the chapters on various areas of the country, Northeast, Southeast, Midwest, Pacific etc., are wonderfully written. AND it is on sale from AHS until the end of this year. (hope the link works, it is from the AHS store)
https://daylilies.site-ym.com/...
If you can find copies another "book" no longer being printed was the EUREKA Daylily Guide. This was a large much anticipated yearly publication with listings from sellers for thousands of daylilies with prices. Included were many color images, but little reading... unless you like reading price lists.
For general information on daylilies two smaller books -
The Daylily, A Guide for Gardeners by John Peat and Ted Petit with color images.
Hemerocallis Daylilies by Walter Erhardt a German author which also has an interesting section on the species with an identification key.
This is just a sampling of the books I've personally seen and have enjoyed reading over the years.