Many people think that spruces, Douglas-firs, and the true firs look alike. In a general way they do, but look closer. Feel the needles. Spruces have stiff, prickly needles, while Douglas-firs and true firs have soft, flexible needles. Each spruce needle springs from a tiny, woody peg; in fact, this peg is one of the best ways to identify a spruce. Spruce cones hang down from the branches like Douglas-fir (remember that true fir cones stand up), but spruce cones do not have Douglas-fir's pitchfork bracts. The scales of most spruce cones are papery thin--yet another difference. And spruce bark is scaly--Douglas-fir and the true firs have ridged bark.
There are approximately 40 different species of spruce in the world, but only 3 are native to the Pacific Northwest--and only 2 of those are common. Location is probably the best clue to their identity.
For more information on the spruces native to the Pacific Northwest, go to the species page or see p. 42 of "Trees to Know in Oregon".