Another thing I would keep in mind when picking out fish is watch them for a little first, don't just pick something because it's colorful or looks 'neat'. Sometimes after you watch them for a while you may not like how they act, i.e. find them slightly boring. There are people who won't touch schooling fish because they can be very flighty and often just swim constantly in a group, while others enjoy that schooling behavior very much. It really depends on what you like.
I've actually found quite a few aquarium videos on YouTube, this may be a way to check out fish that perhaps your store does not carry but still interest you.
Also, ask yourself what you want out of the tank. Do you want a lot of small fish, a few larger ones, or a mix? Community tank or predatory one? Lots of activity or something a bit calmer? Do you really have your heart set on plants? If so, some fish will not be a good mix, as they'll love eating everything you plant.
Once you decide what you really like, research research RESEARCH!!! Find out what their water and temp requirements are, what they can and can not go with, whether or not they need to be kept in groups, pairs or as a single fish, what level of the tank they swim at, feeding requirements, and if they are suitable for your size tank. Once you figure this out you should be well on your way to choosing stock you will be happy and knowledgeable about owning.
One last thing, remember, no fish is a 'tank cleaner'. They may eat food that falls to the bottom, or clean that pesky algae off the glass, but they add to your stock, and they will need fed just the same as your other fish (esp. when the algae runs out
) No fish will eat poo and keep your tank clean.
If you only want a fish for it's 'cleaning' ablilities, don't get it. Poo can be gravel vac'd, not overfeeding will solve extra food and less light or a an algae scrubber will take care of the green stuff.