This is Dame's Rocket (Hesperis matronalis) most beautiful of all beautiful roadside weeds. It's not native, and a bit invasive, and so I was able to justify pulling armloads and armloads one insanely hot June morning (two years ago) for our wedding. It was in bouquets and vases and pimped-out drywall buckets. On tables and buffets and altars and in the bathroom.
It smells spicy, and a little sweet. It smells like summer. It smells like walking down a mile-long aisle carrying flowers, wrapped in eighty layers of tulle while sweat drips down the backs of your knees. At least, that's what it smells like to me.