Grouped by (kind of) distance from Fort Collins with closest first. Asterisks next to the ones I think you should definitely visit.
*Aqua Imports - Great hardscaping, plant, and shrimp selection.
Exotic Aquatics - Decent hardscaping selection. I don't recall any plants or shrimp.
About Fish - Poor hardscape and plant selection. Decent shrimp selection.
*Fish Den - Good hardscape and shrimp selection. Plant selection should be cautioned because they have duckweed in many tanks that are selling plants.
Golden Fish Aquatics - Poor hardscape selection and I believe there were no plants or shrimp.
Pet World - Poor lighting, but okay hardscape and plant selection.
*Aquatic Dog - My favorite for many reasons. Plant, shrimp, and hardscape selection is good.
Todd's Tropical Fish - Not worth going. Sketchy feel to the place and very sick fish when I went.
Aquatic Kingdom - Very expensive, but has a nice aquascaping table and nice pieces for hardscaping. Plant selection seems to be growing. Shrimp were out of stock at my last visit. Again, very expensive though and the owner seems to be very "bro" when you're a customer and forgets you afterwards if you need any help.
Tropical Pet Oasis - Probably too far. Very small and doesn't have much. Great prices and willing to special order, but probably not great for just a visit.
Neptune's Tropical Fish - Probably too far, but has an okay to decent selection of hardscaping materials, shrimp, and plants.