I have dozens of herbals and old receipt books. they all have somethings interesting but none really, really jump apart from Herbal drugs and phytopharmaceuticals
http://www.amazon.co.uk/Herbal-Phytopharmaceuticals-Norman-Grainger-Bisset/dp/3887630793
It's not cheap though but it is full of good information.
Best advice is to choose a plant in season near you. Investigate it, try it out, see how it develops over the year, see if it's in the same place next year, and when another plant catches your eye, as it inevitably will, do the same with it too.
It can be as simple as roses, edible flowers, wonderful scent, good dye if dark red, hips are an excellent food and oil and vitamin rich; or Comfrey is coming up just now, that's a good one and it'll die back and the only way you'll find it will be to remember where the roots grew.
Cleavers are up now and the dandelions too; any of them will do.
Most folks can carry three or four plants a season in their minds and while still keeping an eye on them, add on another couple as the seasons grow. By the end of a year you'll *know* at least a dozen really well, and the knowledge will grow all your life
This forum is a good place to start too, search, ask, start a new thread; if folk who know something useful are about to read it, they'll answer and the discussion benefits us all
cheers,
Toddy