In reply to stucknortherner:
If you find plants and animals together in one book, it's unlikely to be a very good book. Go for a dedicated wildflower key, and don't feel you have to buy a new one - plants don't change! A cheap second hand copy will be just as good. Check the size before you buy, some really aren't very portable.
I'd always recommend a good illustrated one over a photo guide. I have Collins Pocket Guide to Wild Flowers by Fitter, Fitter and Blamey, and I've never needed anything else.
Animals are easier. A decent photo guide should do the job.