I went to Saville Florists when I first moved to Evanston to find a cactus, and the staff was very friendly as well as helpful. In fact, one of the managers ordered a bunch of cacti because there were none at the store, and he said he would call me when they arrived. Sure enough, a couple days later he called and I went to pick out my little $5 cactus.
I felt that they were really friendly and went out of their way to help you find what you're looking for. The store is cute, and not too small either.
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