I have a 45 gallon aquarium and I would love to have an Oscar because I love their personalities. I know my tank is not big enough though. Is there a fish that has a personality similar to the Oscar but doesn't get so large?
If you mean blood Parrots, they are a man made hybrid. Some folks like them, not a fan myself. They can get a fair size, 8ins or so. A pair would be tight in 45g. You could look into popular, smaller CA cichlids like Convicts or Firemouths. Easy to keep and good interaction as well. There are many species of dwarf cichlids you could try. Rainbowfish are another option. Google is your friend for this search
That's a tough one, because Oscars are so ahead of other cichlids on the personality curve.
If you can afford them (and are willing to deal with fussy upkeep), discus are beautiful, and have sort of royal personalities. I do like severums a lot - they're like discus without the difficulty - I've had gold and green/wild ones and loved them both.
I have had very personable green terrors and dempseys, but you might get a shy or aggressive one too. I have a mated Dempsey pair in a 40 now, and I love them, but they hide together a lot.
Lastly, you could try a group of smaller cichlids like rams (which I love to admire in other tanks but know ZERO about) or a group of earth eaters (geophagus - ask around to find out which ones won't get too big).