Sailfin Plecostomus
Family: Catfish (bottom feeders)
From: South America (found in groups moving across riverbeds).
Size: Up to 50cm
pH and Temp: 6.5-7.5 and 24-30°C
Food: Mainly vegatarian, they will eat algae, vegtables and lettuce. Very good at clearing up uneaten food from the bottom of the tank.
Tank: A large tank is recommended. 50 gallons+ with lots of hiding places, bogwood, caves and rocks.
What the experts say: Sailfin plecs are nocternal and will roam the tank at night looking for food. For this reason they should be fed just before the lights go out.
Their body is covered with armour plating (apart from the stomache), for this reason they are one of the more suitable plecs for a piranha tank, but they can still be eaten.
Personal Experience: Sailfin plecs have a beautiful dorsal fin (hence the name). They will spend most of the day hiding or stuck onto the side of the tank, but spend the night hunting the tank for food and cleaning the glass. They do however themselves produce a lot of waste and will knock over tank decorations and uproot plants.
They are also quite territorial towards other fish, especially if the plec already has an established territory when new fish are introduced to the aquarium.
Info from Fishbase and things I've read and remembered over the past couple of months and the pictures are mine.