It all depends on what you're looking to do with your tank. Are you looking to do a reef? Most nano fish are reef safe, so you're probably ok on this one. Do you want a fish that is really swimmy? Or one that will dart in and out among the rocks? Do you want something to sift your sand? Are you planning on having lots of inverts?
Biff has given you a great place to start your research. Ultimately, you can ask for opinions and get some great recommendations, but everyone here has their individual preference that may or may not line up with what you like. I would narrow it down to a few that you really like, and then possibly ask for recommendations from that short list. You will get first-hand experience narratives from people that have either kept them successfully, or you will find out that they are really difficult to keep (i.e. mandarins).
Anyway, good luck, and start researching!