+1 for Sajica, they get to 6", get a nice nuchal hump, and act basically like a small midas cichlid.
An Avocado puffer would also be an awesome wet pet that gets to around 4-5" and has a personality.
Don't listen to the guy who suggested green terror. There is a good reason we are saying you should not get a 9" fish (and green terrors get to 12" eventually). I think the common misconception is that people online are just grouches who don't want you to have fun in fishkeeping and only keep tiny fish... not true! It is because fish are pets, not toys, and like other pets, they should have enough room to swim around and have varied territory. Dogs kept in pounds too long go crazy eventually and "spin", I have seen this with cichlids where they will nontop ram the glass or will just sit in a corner forever. Also, the bioload created by a 8-12" fish will require you to do large water changes possibly every day to keep nitrates within a healthy range. You and your fish will both be better off if you pick a species that can comfortably live in the tank. Best of luck to you!