I've always been interested in getting a "feature" cat. I've kept Oscars for over 10 years, and want to get a bigger catfish. What kind of cat would be perfect for a 55g? I seem to only find small catfish or 200g+ size catfish.
Looking for (hopefully) a predatory cat. The tank is not yet set up, I want to find the cat I'm looking for, and then set up and properly cycle the tank, etc.
Also, as for tank mates, they are secondary to the cat. If I can't have any that's totally fine (though the s.o. says that single fish tanks are boring). I am most interested in choosing the right cat for me and then setting up the right setup for him.
Jaguar cat comes to mind. Since they only get to 8" in or so (some sources suggest up to 10"), you could probably house a pair, given adequate hiding places. Regarding tankmates, I think most fishes that are about their size would do just fine. Anything smaller risks ending up a snack.
For a 55, most predatory species will be out of the question because of their large sizes. I'll drop a line if I can think of anything else.