Well, first of all, you obviously have the Unforgivable Curses :
Hexes and Jinxes, while less powerful, are also considered as Dark Spells :
We could probably add other spells, such as Sectumsempra, Morsmordre or Fiendfyre.
There are also some potions identified as Dark :
We could also add dark objects to the list, which are supposedly-normal objects enchanted with a dark curse. Such examples include :
One could also argue that some creatures, such as Dementors or Inferi are dark creatures.
And finally, some practices are entirely devoted to the Dark Arts, such as Necromancy.
All those examples were taken from the HP Dark Arts Wikia page (which I know is not canon, but this particular page seems all right to me), where you can find others examples of dark objects, creatures and practices.