Iowa City's co-op for nigh on thirty years now. Very friendly place. The produce selection is small, but what they have is very high-quality. Very good bulk section. This location is kind of small overall; if you can't find what you're looking for, you might want to check in Coralville.
Pretty health-conscious. The bulk section contains no trans fats, and I suspect they may have eliminated them from the rest of the grocery too (I haven't asked).
Incredible bread, good sandwiches, and a nice selection of wine. Nice soups, too. Vegan stuff is clearly marked and plentiful.
If you live in the area, it's worth investing in a membership. Non-members get a 10% surcharge, whereas members have the opportunity to volunteer and earn discounts (10% for every 3 hours worked a month, up to 30%). Membership is a one-time payment of $60, which can be returned to you if you leave the area.