A 5-10 gallon nano is a pretty nice work tank. They're small, can fit on a desk, and easy to take care of with the proper maintenance. Clownfish, purplefirefish, gobies all make nice fish for the tank.
I was thinking a bit larger than a nano, I want it to be a real feature. Clownfish is another good idea, but I think it would mostly be children and women who are more interested in them. Most of my customers are men, so perhaps something a bit more manly like predators. No offence to any guys who keep clownfish.
You could do a single Undulated Trigger in a 55 or something a little bigger. They are really friendly, look good, and interact with people outside their tank. You just can't have any other fish.
Lots of people like Flame Hawks and blennies, because they swim funny and seem to watch people.
here are some links, though IM sure that some of you are tired of hearing my mouth, err hand..whatever
a BEAUTIFUL grouper that gets big but not too big, only drawback is its price tag, you can find them cheaper than foster and smith though I just use their site for fish pics. http://www.liveaquaria.com/product/prod ... CatId=1698
In my tank, the eye grabber is the seahorses. But if your target is something "manly", then a preganant male seahorse probably don't work too well for ya.
Haha I laughed out loud when I read that as well. Thanks for all your input, I'm thinking of going for either a Lionfish and Moray tank or a Trigger and Moray tank. I was definately thinking of a Zebra Moray and after reading the link that Tackett posted I'm sold on them. Would two Zebra Morays and two Lions (preferable Volitans but possible a smaller species) be too much for the tanks I'm looking at? I figure that so long as my filtration is good enough, space shouldn't really be a problem.