While Oscars are great fish they can and do get very big and will therefore put a strain on both the bioload and on what other fish you can keep. While Oscars are not too agressive when he/she gets to be a foot long+ it will probably kill any other smaller cichlid in the tank. If you want Oscars I would keep the tank as a species tank and try to get a pair. They grow very quickly.
Jack Dempseys and Green Terrors are both smaller than Oscars but can be quite aggressive (though there are far worse Cichlids for aggression!). In a 72 gallon they should be fine to get one of each and some other fish. You could add another tough medium sized cichlid such as a Convict (smaller but tough) or a Blue Acara or a Firemouth (but these are relatively weak) or a Jewel. Just make sure there are plenty of caves / cover so each can stake out a home and have a selection of refuges for when they fight.
Alternatively go for more peaceful cichlids such as Uaru, Severums and/ or Eartheaters (Firemoths and Blue Acaras are probably OK with these too). These should be OK together unless you obtain pairs and they breed.
You are probably better off adding extra none cichlids though. A bichir should be fine in that tank. As would three or four toughish loaches such as Modestas. A Bristlenose Catfish or two will help keep the tank algae free and not overload the tank (unlike their larger relatives the Plecs). A synodontis catfish (pretty much any sort) should be fine too, or a Dora Catfish (but they are very nocturnal) or two.
IMHO a 72 gallon is a good sized tank for most cichlids, including a cichlid community. You have a lot of choices. Bare in mind that if cichlids breed their aggression goes up a huge amount, so getting singletons is probably not a bad idea. While many cichlids can be ranked for aggression, there is always the odd mean one or dove. Also while Oscars (and other huge foot+ cichlids like Jaguars) can become excellent pets, they are extreamly messy putting a strain on the best filtration and even the peaceful ones are very strong and can kill just about anything you put in with them if they 'turn'.
Good luck! I envy you your tank - I'm sure it will turn out great
