I've had pretty good success with glyphosate on Poison Ivy.  Use some non-ionic sufactant (or cheap dish soap if you are hand spraying) to help it work better.

I usually carry a sprayer, couple 2 1/2 gallon jugs of water, glyphosate, and a jug of soap in the truck during the summer.  Last year I went to Wal-mart and bought the cheapest liquid laundry detergent and used it as an additive.  Worked well and everything smelled summer fresh .