If its out and out aggression (i.e doesn't want you in his territory and will attack the glass if you go near it) you are looking for then the suggestions so far are pretty spot on and a Jag would be my pick of those too.
If you're looking for a fish that has personality, then you can't beat Oscars. They have great personalities and you could keep two in a 90g. My two Oscars are always after my attention and will follow me up and down the tank to keep eye contact with me rather than wanting to chase me away.
I would go with a jag they are agressive and have awesome personality in my experience. If you want to put two or more fish in I would recommend something less agressive. Red Devils are good too but there only tank mates should be rocks. I would start with a small jag they grow extremely fast. I would say at least a half inch a month maybe more. Also the black jags you see are probabally super stressed mine was black when I got him but a few days later he was fine and now he is beautiful with blue in his fins and already showing the purple shade throughout his body just a cool fish.
I dont consider jags agressive, just territorial. Mine is 15" and lives peacefully with pretty much anything I put in the tank. He does have his own territory however. The most wicked fish I've owned that would go in that tank was my vieja fenestratus. It was just evil mean and had some pretty cool teeth too