I have a similiar situation that you have, and with rocky, clay soil to boot! I have found two shrubs so far that don't mind being in the shade under pine trees: a oakleaf hydrangea and a red twig dogwood. It took about a year or so for them to get established, but they are now growing quite happily.
Besides those two, we have a lilac and a japanese maple that are growing next to the pine trees in shady-ish spots. They also might not mind being under the trees.
I hope this helps a bit!

There are actually quite a few to choose from for Northern Climates. Evergreens include many arborvitae but Techny 'Arborvitae'is the most shade tolerant. They really won't grow that much so buy the height you need and be sure to feed and water these ones. For Taxus you can include Hicks Yew, Capitata Yew, Cuspidata Yew, Taunton Yew. Although they are slow growing, they are tough as nails. Buy them as big as possible. Or try Canadian Hemlock but make sure you can keep the soil moist especially during the 1st month after planting. For Deciduous shrubs you could choose, Witchhazel, Redbud, Pagoda Dogwood, Winterberry, Viburnum Dentatum, Viburnum lantana, Viburnum lentago, Viburnum trilobum, Euonymous alatus 'Chicago Fire' or Tures, Kerria japonica, Northern Bayberry, Snowberry, Clethra, Gray Dogwood, Aronia Chokeberry and Amur maples. All of these will tolerate shade very well but will grow in a more open habit, have less flowers and less fall color. Plant in layers to create the desired screening.

Karl

I have 100 ft of pine trees all that have been cut up about 8-10 feet by the previous owner, is there a tall plant or tree I can plant amongst the pines for privacy? Something that would get wide(3-4 ft) and tall (15-ft or taller), for privacy around a pool?

Holly would be your best bet. It's an acid tolerant, somewhat shade tolerant understory plant.

Mountain Laurel in theory should work, but I find them hard to get established.