The Iowa Digital Library is another of the many I have discovered. This one contains more than 200,000 digital objects—photographs, maps, sound recordings and documents—from libraries and archives at University of Iowa and their partnering institutions. Of the many available on the site the following I found to most interesting and have certainly genealogical applications:
1. Civil War Diaries and Letters Digital Collection
2. Mujeres Latinas Digital Collection -the lives and contributions of Latinas and their families to Iowa history
3. Historic Iowa Children's Diaries Digital Collection
4. Hixson Plat Map Atlases of Iowa -Iowa land ownership maps from 1930
and while not genealogical, you might find the Mildred Wirt Benson papers interesting. She's the author of the Nancy Drew novels. Here's where you'll find the collection.