My personal favorite Poison Ivy is Uma Thurman from the movie
I love love love her costume based on the original design. Just look at it.
Watching the movie, I thought the leaves were covered in glitter, but these pictures show that they are all individually beaded (as are the leaves on the sleeves). It's the kind of thing that must have been a pain in the ass to do, but the results are really remarkable.
The vine and leaf detail on the tights was another thing I noticed for the first time in this pic.
I really appreciate when there is that much attention to detail in the costuming, especially in an adaptation.