Pixies are neat creatures.. They aern't evil, but perform quite unkind tricks, like leading travelers astray or to steal naughty children. They like to pinch maids who don't keep the house clean. They were often thought to be the souls of babies who had died before baptism.
Leprechauns. Shoemakers for the noble faeries of Ireland. They were cranky, solitary, and strangely enough, often seen by humans. A caught leprechaun tricks his captor into releasing him by telling him he can show him the way to the shoemaker's great golden treasure, which the sad captor will never see, since the leprechaun will disappear before you know it...
Trolls. Nowadays, we often think of trolls as big, clumsy creatures who go around hitting people on the head with a hammer or something, but in the Middle Ages they were thought to have magical powers as fortune-telling.
Asrai are small, delicate water faeries. Fishermen might catch Asrai with his catch. When exposed to air they melt, leaving nothing more than water behind.
Brownies come out at night to finish work that's been left unfinished. They are devoted to their household and expect nothing but a bowl of cream and a cake for their concern. Any offer of reward or clothing will drive the brownie away. Boggarts are "evil" brownies, they've often have been wronged by humans. They like tricking humans and often cause a great deal of trouble.
Changelings are fairies taking the place of a human child who has been stolen by other faeries. (in some stories like Scandinavian ones, changelings are Troll children) Parents may recover their own child if they can trick the changeling into revealing it's age.
Selkies are faeries who put on seal skins and appear to be seals as they travel in the water. On land they shed their seal skins and have human form. A selkie maiden can be won as brides by stealing their seal skin as it lay on the beach, so they couldn't return home.