These cards come in Chocolate Frogs candy (along with a chocolate frog, presumably). The faces on the cards are famous even to Muggles, although their magical abilities were not always recognized by the non-magical community.

Agrippa
Heinrich Cornelius Agrippa von Nettesheim, 1486-1535, German mystic and alchemist. (web link)

Circe (SEER-see)
Circe, in Greek mythology, is a sorceress who lives on an island called Aeaea, near Italy. Circe was able to turn people into beasts. (web link)

Cliodna (CLEEV-nah)
Celtic Irish goddess of beauty, the eldest daughter of the last Druid of Ireland. 

Grunnion, Alberic
Could possibly be in recognition of 'Alberich,' a powerful wizard from "Song of the Nibelungen."  The poem is mythical, but was the basis for Wagner's Ring Cycle. In Wagner's version, Alberich makes a ring from gold that he has found and places a curse on it against its thief!  Interestingly, one of the prizes given to a 'hero' of the Ring Cycle is an Invisibility Cloak. (contributed by Adrian Allum)

Hengist of Woodcroft
Hengist was a Saxon King of Britain shortly before King Arthur's time, who helped King Vortigern defeat Scot and Pict rebels. Later, he lead a rebellion of his own, and eventually founded the county of Kent. Quite what this has to do with wizardry, I don't know, but David Colbert offers a similar suggestion in his book, "The Magical Worlds of Harry Potter." (contributed by Adrian Allum)
NOTE: In the Harry Potter computer games, Hengist is described as living in Medieval times. He was persecuted by Muggles, presumably in England, left for Scotland, and founded the village of Hogsmeade. Many believe the Three Broomsticks Inn was his old home. This information is not canon, but is included as a matter of interest.

Paracelsus (par-a-SELL-sus)
Alchemical genius. Auroleus Phillipus Theophrastus Bombastus von Hohenheim, known as "Paracelsus," was born in 1493. (web link)

Ptolemy  (TOL-uh-mee)
Claudius Ptolemy, born c. 85 AD. Geographer and astronomer. (web link)

Dumbledore - 
Current headmaster of Hogwarts, renowned as the greatest sorcerer of the present age.

Merlin
Wizard, famous for his role in the King Arthur chronicles. Tutored the young Arthur before he knew who he was and what role he was to play in history.

Morgana - 
The famous Witch Morgana, like Merlyn, figures into the King Arthur legend.  According to the legend, Morgan le Fay, or Morgana, was the witch in the castle that Wart and Kay encountered with Robin Wood (Robin Hood for the unenlightened), Maid Marian, Little John, and the merry men to rescue Friar Tuck, the Dog Boy, and an old man named Wat. Morgana was the child of the Duke of Cornwall and Igraine, the woman Uther Pendragon seduced to have Arthur. (contributed by William Givens)

Real Harry Potter cards are available in several varieties. There is a Harry Potter Trading Card Game from Wizards of the Coast, trading cards of the film, and Chocolate Frog Candy with collectable wizard cards inside. None of the information on these cards is considered canon unless is matches information in the books or interviews.