Giant's Toe was the first I thought of. And human heart/flesh (I don't even eat that in the game!) Having read this thread I'd like to add Spider egg, Chaurus egg and Falmer's ear on the list. Troll fat doesn't sound too appeasing either, though I suspect it's one of those ingredients the future Skyrim food industry will use in the products and give a nice clean number so you don't think about what it actually is.

Oh, and I'm not sure about butterfly wings.
Oh don't be squeamish. I'm pretty sure that anything that is edible in any extend that got passed under a fire would actually taste good. Chaurus and spiders' eggs would be popping with taste. Giant toe would have a smoky flavor. Troll fat actually looks like a bowl of rice pudding; pour it out on a pan, do it over with some mead and spread in on bread.
And Charred Skeever Hides are popular food, also packed with beneficial bonuses and no poison effects. So I would imagine Skeever Tail's being something as such when properly cooked.