Your definitely starting off right by going to petco and petsmart rather than a place like Wal-Mart. I personally have never had any luck with fish from a superstore, and havn't heard many good things from others either. Now, onto your fish... It really depends on your style and the size of the tank. If your going to want room for them you should have at least a 20 gallon, but I have had a successful tank with just a 10 gallon. Some of my favorites are sharks and catfish. The black tip sharks have alot of personality and go really good in groups of 3! They are a blast to watch swimming together! And contrary to the shark name, they are completely harmless to other fish! Same thing with pictus catfish. I'm not sure about buying them in groups having the same effect as the black tips that tend to swim together most of the time, but they do have a stunning appearance and are fun to watch swim. These fish are mostly bottom swimmers though so you would want to get some fish that are actually going to swim around the tank too. Another shark that tends to swim around the tank alot, and is also non aggressive towards other fish is the iridescent shark. They will need bigger than a 10 gallon tank tho. They are another cool swimmer. A cool fish in general is a silver dollar, but like the iridescent, i think you will definitely need bigger than a 10 gallon for these guys. They are a larger fish and they are all bright, shiny silver! Clown Loaches are fun to watch because they are full of personality and they are goofy! They dont need such a large tank, but they do need places to hide because they are shy. And algae eaters are always a help too! Hope this helps!