Because as soon as you start really looking, a lot of plants have three leaves and sort of look like poison ivy, and poison ivy itself is variable enough that it can be hard to pin point other identifing features that seperate it from these look alikes. So I've been thinking for awhile of a quick, nontechnical guide to separate Poison Ivy's look a likes from the plant itself.
The plants pictured below are prime candidates for Poison Ivy look alike status. Under the plant's name is a one word or short phrase description of the plant; one feature that distinguishes these three-leaved plants from Poison Ivy. Then after the picture is a short discussion of that feature. Note these are not complete ID guides for these plants.
Box Elder - Acer negundo
Raspberry - Rubus sp.
Virginia Creeper - Parthenocissus quinquefolia
Hog Peanut - Amphicarpa bracteata
Jack-in-the-Pulpit - Arisaema triphyllum
Note: the five plants included here may not be definitive, since most of my experience with the plant is from MN. I'm curious to know what other plants you know of that look like Poison Ivy.