Your tank would be large enough for a silver or a black for a while as other people have said, but I would not go with a Jar because they are just too violent. If you can find a Lei they are absolutely gorgeous, but they arent available very often around us. The problem with getting a Lei or an Asian is that they aren't flexible enough to turn around in that tank very easily.
There are always other options for cool preds in your tank. Keep an eye open at the LFS or online, at least around Chicago we have been seeing some really cool catfish coming in more often, as well as other random preds and cichlids.