I have three books.
Songs for singing & musicianship training by David Vinden and Yuko Vinden
This is an excellent reference book and has lots of songs in it slowly increasing in complexity
Jolly Music for Beginners by Cyrilla Rowsell (our very own forumite) and David Vinden
This book is a comprehensive classroom scheme for Early years and KS1 classes. Although I've used it to good effect with pre-schoolers. The songs in this book are also contained in the first book I mentioned but in this book they've been made into a full scheme of work with detailed lesson plans. It also has CDs. I love it and think it's great but it's not the best resource for learning about Kodaly yourself since each book only covers a small amount of content. However it's great for identifying creative ways to be repetitive with the skills and information.
Go for Bronze/Go for Silver/Go for Gold
I have the teachers books and the student books for these and they're great. Aimed at children aged 7 up. Again they make up a scheme of work aimed at singers and are a great way to teach singers how to read music. They're split into lessons and each lesson has a double page spread in both the student book and the teacher book. The teacher book has a picture of the lesson book page and is surrounded by teaching tips. If you were learning yourself then you could either get the teacher book (expensive) with the full explanations, or get a student book (cheap) and take an educated guess.
I haven't done a Kodaly course but I'm sure that Barry is right and the best way to learn is to do a course. It's just I can't spare the time at the moment. Personally I'm finding the Go for Bronze series the best for my own development right now. But I'm glad I have all three of the books mentioned above because I do dip into all of them from time to time. My singing students are loving the Go for Bronze series and I'm trying to adapt it for my piano students too.
Plus of course a PM to Cyrilla is enlightening.