Yarrow

Other names are old man's pepper, soldier's woundwort, knight's milfoil, herbe militaris, thousand weed, nose bleed, and carpenter's weed.
Is known to grow in grassy areas, roadsides, and meadows. It can grow in very bad soils. It will grow from 10 to 20 inches long. It has a very feathery leaf base and a cluster of flowers. The flower is white and blooms around August.
In the past it has been known to be used for divination. Because of this, the random number generator for computers is named after that. It is used medicinally for many many bodily issues. It is easiest to just use it in your tea for flues and cramps and such. You should dry it, and use one teaspoon for each cup and let is seep for around ten minutes.
In the past it was a herb dedicated to "the evil one" so many of the old names have the devily sort of names.


References:
http://www.botanical.com/botanical/mgmh/y/yarrow02.html
http://www.schneier.com/yarrow.html
http://www.altnature.com/gallery/yarrow.htm