The second and third of these are technically not roadside plants, but the first one is:
I don't recall ever seeing it before, but they're everywhere all of a sudden.
UPDATE: it's a Vernonia (ironweed), possibly V. baldwinii. Thanks to Claude and joeym.
The other two plants were in a heavily wooded park in Iowa City about a week ago. The first, I'm fairly sure, is some kind of Arisaema. I don't know if it's possible to narrow it down to a species from these pictures or not.
UPDATE: Everybody seems pretty convinced that this is Arisaema triphyllum (jack in the pulpit). Thanks to Ed Kramer, joeym, and anonymous.
The other plant from the park has flowers reminiscent of both chicory (Cichorium intybus) and meadow campion (Silene latifolia), but it's not either of those. Something related?
UPDATE: Looks like this is a Lactuca sp., possibly Lactuca floridana. Thanks to The Phytophactor and Review for their help.