Though the Marauders play a tiny role in the book series they are the stars of many a pairing. Wolfstar (Sirius/Remus) in particular is popular with those who want more freedom to come up with their own stories within the HP world.
Given the popularity of the good/evil trope, it is unsurprising that HMS Leather and Libraries has such a following. Many of these stories involve Draco Malfoy learning to help the light through falling in love with Hermione Granger.
Usually relating to time turner or post-Hogwarts fics due to the age restrictions, Severus/Hermione fics are very popular within the fandom. The pairing seems to emerge from Severus Snape's preoccupation with Lily Evans, perhaps because Hermione is…