I managed to stick a jack Dempsey with mine. It's reallyrare that these two fish get along together, so I wouldn't try it.Plecos are a good choice. So are most medium-sizedbottom-dwellers.
Now, I haven't hear anyone suggest this yet, but dependingon how big your Oscar is, you could put adultconvict cichlids in with it. I have 3 in the tank with mine, and I had a parrotcichlid until it died of age. But myOscar is a wimp. My pleco bullies him. So I don't know. Depends on your fishand how big the convicts are. You would have to buy full-grown convicts foreven a 8" Oscar.
Silver dollars are another good idea. Great-looking, ratherpassive, and they can bring a lot of life to the tank.
Let me think...another idea would be to buy a second O. Theymay not get along, so its hit or miss. Jade eye cichlids are also supposedly agood choice. Severums too. Chocolate cichlids, Blue Acara (as adults) andFiremouths are all a great idea.
If the Oscar is 6" anything under 3" Will be food.8" anything under 4" would be food. so for a full-grown, you're gonnawant nothing under 6"