Best Local Fish Store within 100 miles of CU. There are others with better selections of niche products (such as Johnny's Reef Experience in Normal has better coral), but Sailfin is the overall winner, especially when it comes to fish. Their prices are not the lowest, but it is not cheap to stock a large selection of healthy animals and maintain an educated staff.
If you have questions, the staff are very good about giving you a straight answer, even if that means dissuading you from making the purchase. Sometimes it can take a while to get service, but this is just b/c this sort of consultation takes time, and once they get to you, you will appreciate the personal attention. If any staff members are in doubt about a question you may have, they send it up the chain, all the way to John if necessary.
Speaking of John, he genuinely takes an interest in every hobbyist that comes through the doors and wants the best for all. Don't tell him that you got your equipment or livestock from other sources, such as craigslist or Internet forums, as he poo-poos them. This is because he dislikes the anonymous nature of this stuff (and maybe a little competitiveness no his part).
They have a 1 week guarantee on their fish (but not invertebrates) and have sales from time to time on their website. When they have these sales, it is not to clear out existing inventory, but to generate volume, so they stock up huge in advance of them and are thus a great opportunity.