It helps a lot to know a person's budget and experience before recommending any fish. There are so many awesome fishes, but which one to keep all depends on the aquariat's skill level. In general, but certainly not always, if one needs asking what the rare or expensive fish are, then they may need a little more experience in the hobby. There are plenty of "look at my kewl fish that most of you can't or don't want to afford" threads in the reef fish forum, but on the flip side there are plenty of great fish that do come in at less than $100 or even $50, and just like many of the more expensive varieties the require a higher skill level and patients in finding them.