The ASPCA also has a non-toxic list on their website.
If I have a chance I'll see if I have some of my favorite databases bookmarked. I like looking for databases that discuss the degree of toxicity, since while some plants listed as toxic are deadly and clearly shouldn't be anywhere near a cat, others fall into the "your cat will barf if she eats it" category and those I'm personally more lenient with. (For example, I have an amaryllis that predates the cats. They're apparently mildly toxic, but Stormy leaves it alone -- I don't know if she can sense it's not good for her or just doesn't like the texture -- so it stays.)
The impatiens seems to have migrated from the "non-toxic" list to many "toxic" lists between last summer, when I first bought them, and this summer. I don't know much about impatiens but I know Stormy ate a whole one leaf by leaf over the course of last summer with no apparent ill effects.
She seems to be preferentially going for the cat grass now, thank goodness.