The family Balistidae is extremely varied. Some Triggers, such as the Undulate, are viscous beasts. Others, such as Pinktails, wouldn't hurt a fly, and are even reef-safe.
The Triggers I have read about and think are not ideal, but can be accomodated in a community/reef tank, are listed below.
Genus Melichthys
Pinktail Trigger (Melichthys vidua): Very docile Trigger with a pink or orange tail. In my experiences, will ignore small crabs and shrimp, unless when very hungry. Will pose for Cleaner Shrimp (Lysmata amboinensis/grabhami). Is more "cute" than pretty, but still is very handsome with it's green body and clear, black-edged dorsal and anal fins. Often said to be the best species for a reef tank, but a large tank is needed (100 gallons plus)
Hawaiian Black Trigger (Melichthys niger): tends to be a little more aggressive than the Pinktail, and grows larger. They have very beautiful colouration. Grows to more than a foot and a half, so again a large tank is needed.
Indian Black Trigger (Melichthys indicus): grows much smaller than the former species (25 centimetres), and like the Hawaiian Black Trigger, has very beautiful colouration. However, research suggests that M. indicus may be less ideal for a reef tank than the others, because they feed from the sustrate and rocks rather than the water column.
Genus Xanthichthys
All Xanthichthys (Crosshatch, Bluethroat, Sargassum, Striped, Bluelined) have been called "suitable for a reef tank". They all tend to be docile, and all of them have very beautiful colouration (The male X. mento is incredibly highly coloured) and have a pleasing "torpedo" shape. While they aren't the most hardy of Triggers, they still rank very highly when compared to other marine fish.
Genus Odonus
Redtoothed or Niger Trigger (Odonus niger): the reef-safeness of these animals is debateable. While generally docile, there are some "bad eggs". They are very desirable, with their beautiful blue/green colouration, which varies directly with the angle they are viewed at. They also have a pleasing "torpedo" shape, and a lyre-shaped tail that can occasionally grow very long. They have very strong, sharp teeth and can very easily latch on to fish nets or fish bags, piercing the bags and causing them to leak. They also exhibit the ability to blow jets of water (even when caught and out of water - watch out), suggesting a highly predatory, lobster-and-urchin diet, but they actually prefer to feed from the water column. Their sharp teeth and bold nature means these fish need to be treated with caution, as they can bite fingers, easily drawing blood. They will pose for Cleaner Shrimp.
-Lynden