Ledges State park north of Des Moines and south of Boone is very nice. If the lower ledges road is closed then its a bit of a hike. They close the road when the river is high because it floods. Before you get there you should drive by Saylorville Lake and the High Trestle Trail Bridge.
Conversely Pella, to the southwest, is a charming dutch town that has quite a bit to photograph. Lake Red Rock, in the Pella area, also has some nice vistas available. As far as small towns and farm land... that's pretty much all of Iowa outside of the cities. Just stay on a smaller highway for a bit and you will see copious amounts of both.