Tecnu. You should try to find this stuff called "Tecnu". You can get it a REI and I think some drugstores. It so much better than everything else out there - helps you heal fast! And now i always shower with it after hiking b/c it takes the oils off your skin just in case.
Poison Ivy/oak. The best thing you can do if you know you've come into contact with ivy or oak is to scrub yourself with water and soap. You can get away with this remedy until about 15 minutes after contact. After that, you're going to need something stronger.
If you want to go natural, cut open an aloe plant and rub the aloe onto your rash. If you don't care what you put on it, Calamine lotion is always the way to go.
To stop the itch, you can make a white vinegar mixture 1/2 cup vinegar, 1.5 cups water and dab that on your rash, or dab cold milk directly onto it.
In general? When you go into the wilderness, cover up!
Tecnu. Definitely Tecnu. Let's just say I have this friend who recently got poision oak. Put Technu on for a few days after it showed up and it completely disappeared. It basically gets under the poison and somehow pushes it out of your skin...
Here's a link to the company's website if you want to learn more about it.