I spent some time this past weekend dyeing with coreopsis. They are tiny little flowers but hold a lot of color. They're a few different varieties, the type I used was coreopsis tinctoria, I've noticed if the Latin name for the plant has tinctoria in it, it is a great dye plant.
I simmered them about a hour then put the wool fabric in, it became a beautiful peachy orange color right away.
And cotton fabrics. They seem to take the color the same as linen.