Tipalia Buttikoferi

Want the Oscar got killed?? That thing is way.....tooooo aggressive.
Getting tankmate for your Oscar...always consider his/her aggressive level. Some Oscar gets quite aggressive. Some extremely laid back...even live with big GoldFish.
Also, if you feed your Oscar feeders, it is a mess, and your oscar will end up eating the tankmate that you put in if it is small and can't defend him/her self. If you want to feed your Oscar meat, consider making him/her homemade fish recipe. It is healthier.
Tankmate for your oscar has to be about the same size when fully grown. If not the same size...and least that guy knows how to defend him/herself.
Again this is suggestion. Do need to consider your Oscar's aggressive first.
Uaru Amphiancanthoides (peaceful but very big. consider peaceful giant. can get to 12")
Blue Acara (DarthV already mention, but this fish gets about 7" max even though I haven't seen one with that size)
Copora Nicaraguense (DarthV mentioned this too, but this fish is small as well when fully grown)
Blue Dempsey/Jack Dempsey (Blue is more peaceful than Jack...both don't get as big as Oscar...7/8" max for Blue. 10" max for Jack)
Another Oscar (which you mentioned)
Firemouth (doesn't get very big. 7" max that I've seen)
Green Terror (Gets to 11" max but usually less than that. tail and dorsal fins with red/orange highlight isn't as aggressive as the white/gold highlight...so I heard)
EarthEaters (there are many species in that category. find something that can defend themselves)
Severum (I will go for male who can defend himself. My Green Sev always pick fight with other fishes)
That's the most that I can come up with. Hope that helps.