Black Saddlebags (Tramea lacerata) are one of the species of North American odonata thought to be at least partially migratory. They are common here, and although I can't say I've observered anything that appeared to be migration, I have seen large congregations of them.
At a large, scrubby open area near the Detroit River on Labor Day, Stylurus and I saw hundreds of Black Saddlebags. They were both in the air hunting, and many were perched in the vegetation, like this one. There were a couple of Carolina Saddlebags with them (we were hoping for the rarer Red Saddlebags, T. onusta, but the one we caught was T. carolina), and many Pantalas. Normally, Wandering Glider (P. flavescens) is the more common species, but in this group Spot-winged Glider (P. hymenaea) outnumbered them; it's been a bumper year here for that species.
Update on dragonfly migration: A nifty paper was published in 2006. The abstract is here and a summary appears at Science Daily.
It's also been a decent year here for southern butterflies. Nectaring on Eupatorium (mostly tall boneset) were at least a half-dozen Fiery Skippers (Hylephila phyleus). This is a species just at or beyond the northern limit of its range in Michigan. Some years it's fairly common, while it is absent in others.
It must be autumn.