Please let me know about any fics you feel belong on this list!
Hermione goes back
1) Deception & Concealment by KissThis
Summary: Voldemort is dead; Harry bitter. In order to save him and her world, Hermione does the unimaginable and the illegal - disguised as a boy she goes back to the Marauders' Era, but finds herself in a sticky situation of love.
Pairings: James/Hermione/Sirius (threesome, not triangle)
2) A Gift of Time by Leraiv Snape
Summary: "Granger, Hermione." None of the students heard the catch in Professor McGonagall's voice. And even if they had, they would have attributed it to dryness of her throat, not to sudden shock. Before them, in the space of breaths it took to say her name, Severus Snape, their colleague of thirty-one years had dissolved, leaving a blossoming adolescent of seventeen.
3) Somewhere I Have Never Travelled... by Savageland
Summary: *Completed.* More than thirty years after a mass-killing curse devastated Hogwarts, a mature Hermione makes a life-threatening journey back to that time, hoping what she’s learned will save lives. Taking the alias "Gwen Hawking," she finds her mission further complicated by a passionate, conflicted relationship with a much younger man--Severus Snape--and the distrust of her eighteen-year-old self. (Pre-HBP; OOTP compliant.)
4) Time Revolution by KissThis
Summary: Hermione's ritual magick brought back four people from the past to fulfil a prophecy, but they aren't exactly the four she planned on. Are the trio a prehistoric triumverate of power? Will Voldemort be defeated? Love for the Marauders?
Note: I'm allowing this one because the ritual was used on purpose to bring someone from the past.
Multiple people go back
1) Have You Ever by Lady Moonglow
Summary: With the war looking bleak, the Golden Trio, Ginny, Draco, and Lavender go back to Tom Riddle's 7th Year to destroy Lord Voldemort once and for all. However, Hermione DIDN'T count on a shared common room, a curse, and a little thing called love.
Pairings: Tom Riddle/Hermione