This is sort of a follow-up to my previous post, about butterfly shade plants. Apart from the ubiquitous Buddelia, what other shrubs have you found useful for nectar? As Misssherry said, spicebush and Wafer Ash are good host plants for specific butterflies.
I just planted a bottlebrush buckeye, which is supposed to be a butterfly magnet. It also favors shade. My understanding is that buttonbush is a great choice, too, although it is a "head in the sun, feet in the wet" sort of plant. I have lots of other shrubs planted, but I don't know if they are particularly attractive to butterflies. I have viburnums, Fothergilla, Clethra, serviceberry, azaleas, and some other things I can't recall at the moment.