Berry Fresh Farms has strawberries, raspberries, & blackberries for picking or purchasing throughout the year, in addition to a small farm store.
Iowa Orchard has a few locations; this location has pick-your-own apples but no other activities. There is no admission fee; you pay by the weight (two different size bags). There is another location in Urbandale with fun activities (but no u-pick apples).
This is also the location for u-pick strawberries during summer.