I bought Paula Pryke's Flower School: Mastering the Art of Floral Design a while ago and have been dipping into it at leisure. Some of the arrangements are more "floristy" than I would ever attempt, but there's plenty of simple loveliness too and the instructions are amazing. If you're looking for a flower arranging book, I recommend it as a close second to this, which is still my most favourite.
Visit Paula Pryke's website here. Photography by Sian Irvine.