I lived in PHX for ten years and agree totally, the Oceans Floor is great when you are in a pinch because it has everything you could think of but they charge sooo much. I've definitely shopped there more than a couple times and then gone on the interweb to buy what I liked at a bargain price.
If you are looking for livestock, there is a small privately owned place up just north of camelback and I want to say 16th street (I've been back in Maine for 2 yrs so my memory could be better on this). It's in a neighborhood and behind a apt building, really terribly placed. But the woman who owns the place rocks and they usually have a bunch of great fish in.
FINALLY!!! I actually have some planted tanks!!