If you find a good used book store, you can find great aquarium books inexpensively. Call around town and ask what used book stores have a big pet section. Library discard sales are also great. I've got a library of about 60 fish books!
One that's easy to find is Exotic Aquarium Fishes by Innes. It was originally published in 1938, so it doesn't have any high-tech set-up information, but the advice on individual fish is good and I find myself looking things up in it on a regular basis. I've also got a copy of "Goldfish Varieties and Tropical Aquarium Fishes" by Innes, which came out in 1917! That is a real trip!