Wildflowers of Ireland. This is what got me started identifying wildflowers. I have used the book by Zoë Devlin for all my attempts at identifying, even though (clearly) this is not Ireland. As well as her photographs, the book has classic poems - sometimes several - to go with many of the flowers and it also has the Irish names and folklore, all of which makes the book very interesting and enjoyable. There is also the sense of a personal journey, with the dates and places when all pictures were taken. Of course the technical data is also included, botanical names, distribution, cross-references, recommended reading etc.
Wild Flowers of the British Isles. This looks a good site, which I hope to make more use of.
Here are some quick access sets of thumbnails, to see lots of possibles at a glance:
A-L1 Agrimony to Long Headed Poppy
L2-Y Lords and Ladies to Yellow Flag Iris