Over at Garden Rant, Doug Tallamy comments on native versus non-native plants in the garden for the sake of insects. Most valuable bit: a tree or shrub hosts WAY more insect species than any herbaceous perrenials does. As we all know, when you host insects, you host almost everything else (including birds). So plant those native shrubs and trees! For me, promoting local biodiversity is one of the main reasons to garden. Here's the link.
I haven't done any surveys, but Scrophularia californica (above) has to be one of the best herbaceous perrenials for attracting insects. It bears hundreds of tiny nectar-rich blooms nearly the whole year round and the bees, bee-like flies, and hover flies know it.