Plenty of small catfish with personality or at least interesting behavior - upside down catfish (there's a few species sold with the name - you want Synodontis nigriventris), I recently rescued a Synodontis petricola, and he's a surprising character considering his poor condition. A good sized shoal of corydoras is always a joy to watch.
While pushing your size a bit, bristlenose plecs are active and meet your other criteria, they top out at around 12-13 cm if my conversions are right.
A shoal of tiger barbs or some of the more aggressive tetras - black phantoms, serpaes, etc - are also fun, active fish, though I wouldn't use the term personality.
And kuhli loaches - great fish. Around 10 cm, but very skinny bodied. In a good sized group, they're active and playful. You can usually find them wriggling around in a ball.
Edit: Keyhole cichlids are also a bit over your size - 12-13 cm again, but they have all the personality of the big cichlids, but none of the aggression. They also change color constantly with their mood or surroundings.
