I got a copy of Peterson Field Guides Edible Wild Plants 3 years ago for Christmas. This was my wife's response to my request for an edible wild mushrooms book. Apparently eating wild plants is much less scary than mushrooms.
I must say that this is my all time favorite pastime while camping or hiking these days. I take it on most hikes and trips. There is nothing more satisfying than going for a hike and bringing back a bag full with your next meal. Grant it, sometimes these plants really don't taste very good. Other times, however, they are great. In response to this we have come up with our own "ass-factor" scale that describes the plants flavor in relation to ass. I've started rating each plant as I try it.
The book makes identifying plants fairly easy. Although in most cases you need to have a flower available for easy identification. Winter identification is much more challenging.
I recommend this book whole heartily to anyone who is a little adventurous in what they eat.