The fish that really hooked me in was the common featherfin squeaker. I bought a group of juveniles for my basic 20g office tank, thinking they were the smaller-growing Synodontis nigriventris, and once I realized my mistake I had to return them all... except the smallest, which I took a liking to.
I upgraded to a 55g for that individual fish, and in the tradition of many novice fishkeepers, turned it into a kitchen sink with a bunch of other species I bought on impulse. Thankfully my tastes run towards cories rather than cichlids, so the tank now is slightly overstocked but functional with frequent WCs.
Here's a shot of the syno jetting through the tank - winter is in full swing over here, and he's got a cozy spot next to the heater that he likes to huddle in, but he comes out like a bat out of hell at the slightest prospect of food. You can also see a bit of his exposed gills - I found out later that the reason he was so small is that he's got some gill and mouth defects, including a lack of gill covers.
(Still, a few measly deformities didn't stop him from pigging out so much that you could confuse him for an eggbound female).