Ortho Brush-B-Gon is what we have found to work best.
If you know that you've been in contact with the plant, washing up with Lava soap or any other harsh soap will minimize, if not stop the ivy from giving you a rash. Any tools, toys or clothing that has touched the poison ivy will hold the oil indefinitely and can reinfect you!
Poison Oak is a relative to the ivy, but grows into a bush and is just as troublesome.