Adams Aquatic ,on 42nd street, is the best LFS in Des Moines. They have a good selection of community fish.They usually have a good plant selection.They will also order in any fish or plants you want. They get their shipments on Thursday.
Iowa Pet food and Seascapes(West Des Moines) is good too. They just re-did their fish room. They are mostly into saltwater,they have some awesome display tanks. Their freshwater selection is descent,and will also order anything you want in.
If you can get by the fact that Aqualand looks and smells as if it should be condemned,they have a good selection of cichlids. They will pretty much take anything from people who don't want their fish anymore,so they do have some larger fish for sale. I personally don't go there anymore. The smell of animal urine,and the fact they sell cats has kept me away.
There are also plenty of Petsmart and Petcos around too. The Petsmart in Ankeny has a descent plant selection,and the Petco in Windsor Heights does too.