I agree, if it's not about planted tanks, Oscars have to be the biggest "water puppies" around.
Otherwise my African Butterfly's have a pretty cool personality, as do Betta's, Cherry Barbs and Cory's, to name a few. Of course sometimes it's hard to determine if it's personality or begging for food. :roll:
Chocolate gouramis are great --a little skittish but intelligent, gentle fish overall.
Blue rams are a lot spunkier/more aggressive than the chocolates, but are still quite peaceful and show VERY interesting territorial behavior (get good, locally bred ones). Angelfish can be a lot of fun as well.
Generally, all cichlids and gouramis have loads of personality, actually.
Loaches are also great --I had a friend who had a trio of B. sidthimuniki (dwarf/chain loaches). They were fantastic, as they constantly scrounged around for food, chasing each other's tails, and making clicking noises. They even learned how to latch onto frozen food cubes and stay latched on even when the cube was lifted out of the water (it was really cool to witness this!).
Two loaches on my want list are B. striata and B. sidthimunki. The chained loach is my number one choice, but I have not been able to find or order either one at any store within an hour's drive. I heard a few months back that Absolutely Fish in Jersey had some sids for $20/ea.
I believe they're on the red list at this point.