Mentor

Better Be Slytherin! (Harry Potter) by Jharad17
As a first year, Harry is sorted into Slytherin instead of Gryffindor, and no one is more surprised than his new Head of House. Snape mentors Harry fic.
Nobody Cared (Harry Potter) by Etherian
11 yr old Harry misses the Hogwarts Express. Snape is sent to find out why. What he finds changes any preconceived notions he might have had about the Boy-Who-Lived. AU, manipulative!Dumbledore, DE's, Voldy, but no horcruxes.
Pet Project (Harry Potter) by Caeria
Hermione overhears something she shouldn't and decides that the house-elves aren't the only ones who need protection.
Who Lives in Disguise (Harry Potter) by Duj
It was the longest, shortest trip back from Hogwarts ever. (HBP compatible)

Enemy Within

(1) Harry Potter and the Enemy Within (Harry Potter) by Theowyn of HPG
In his sixth year at Hogwarts, Harry's mental link to Voldemort is stronger than ever. Can Snape teach him to control the nightmarish visions? And is their connection the key to ending Voldemort's reign? (AU, set after OOTP)
(2) Harry Potter and the Chained Souls (Harry Potter) by Theowyn of HPG
Harry must discover how Voldemort cheated death. He faces Death Eaters, shadowy Ministry officials & suspicions that threaten to tear his own allies apart. But the answers lie in the mind where victory can only be won by freeing the chained souls.

(1) The First Prophecy (Harry Potter) by Loxodonta Magica
Snape finds out about another prophecy as he sets out to learn more about Muggles. Harry becomes more to him than just a Hogwarts student.

(1) The Definition of Home (Harry Potter) by Oliver Snape
Harry runs into Snape while trying to find the definition of home, and finds himself drawn into Snape's summer Order task by the headmaster, looking for a location outside of London. Along the way, he and Snape learn a few new definitions themselves.
(2) The Definition of Family (Harry Potter) by Oliver Snape
Now back at Hogwarts, Harry balances school and his home life as he prepares to face Voldemort and learns to trust Snape's guidance. Along the way they both learn that family also means support.

(1) Resonance (Harry Potter) by GreenGecko
Year six and Harry needs rescuing by Dumbledore and Snape. The resulting understanding between Harry and Snape is critical to destroying Voldemort... (AU)
(2) Revolution (Harry Potter) by GreenGecko
Harry continues his Auror training and begins a journey of mastering his unusual and growing powers. Harry, with the help of his adoptive father, is finally making his own way, but fate and prophecy are never completely absent.