The 38 Flower Remedies. It's by Judy Howard, curator of the Bach centre, but this isn't obvious. It's a little orange booklet and pretty cheap but really gets to the heart of each remedy. (It's in alphabetical order too, which is handy.)
Flower Remedies, by Peter Mansfield. An insightful glimpse into the remedies in friendly paperback form. As I remember it (I borrowed a copy from a friend, and must get my own!) it covers Australian Bush Remedies and other systems as well, though the Bach bit is plenty thorough enough.
Either of these will get you quite a long way. I've got several others as well, but they all tend to say the same old thing and give rather 'cartoon'-like descriptions of the mental states. You'll find similar information in nearly any book you buy off the shelf. The best of the rest though is probably
The Bach Remedies Workbook, by Stefan Ball. It's not really a workbook, but there are some amusing dialogues written in the characters of 'typical' people who might need each remedy.
Edward Bach's own writings are available (including The Twelve Healers which I've read but can't remember that well). I only really know
Heal Thyself, by Edward Bach, which doesn't really address the remedies at all, but is rather a background to his view of illness and medicine, informed by his training in homoeopathy. It's a strange combination of trad. Christianity (self-sacrificing morals; 'divine creator' references); Theosophy (I'm guessing); and a distinctively early 20th-century western take on Buddhism (meditation on positive qualities; over-literal version of rebirth). Read it, but don't let it put you off. Most of what was innovative and forward-looking about it we probably take for granted now.
Hope this is helpful! Would love to hear anyone else's opinion/review of these or other books. In particular, I have been recommended the writings of Mechthild Scheffer, and am still deciding which one to order - has anyone read any of them?
Regards, CB xx