I think I saw this one yesterday:
The picture is of a Plains Garter Snake - Thamnophis radix, although it could also have been the Eastern Garter Snake - Thamnophis sirtalis. Anyway, it was like 2 feet long and had a cool red stripe running down its back. Alice also saw one climbing in our pepperplants, which fortunately were trellised to support its weight. I got the pictures from http://www.herpnet.net/, where I also learned about some Iowa frogs.