Personality? Deffinitly a betta. Color? Still ... betta. If he would prefer more than 1 fish or just more activity in general, look into the tiny fish. Guppies (I've not found them to be sensitive at all, but alot of people do), tiny tetras, microrasboras, etc... I really love the galaxy rasboras, but I got mine before they were being overexported, so you might want to hold off on them untill there are aquarium bred specimins available so you are not contributing to their declining numbers in the wild.
I think if he could find a betta that suits him, it would be the best solution. They have incredible personalities, are very colorful, very hardy, readily available and don't cost an arm and a leg (unless you want to show or breed, which I am assuming is not the intent here). A nice dwarf gourami is another option. in a 5gal with either a betta or a dwarf gourami you could probably have a snail and/or a couple otos as well.
If you want to go inverts, shrimp are facinating, as are dwarf crays. Snails are nifty too, but I tend to think of them as secondary inhabitants, not the main focus of a tank.
If he would be able to keep up a planted tank, it is really a rewarding experiance and there are plenty of low light plants that hardly require anyhting more than a little light.
Ask him what he is looking to get out of this tank and we can give more suggestions. (IE: Color, activity, simplicity, etc...)