When one wizard saves another wizard's life, it creates a certain bond between them, a "life debt." James Potter saved Snape's life many years ago, but the effects of it still influence Snape's life. Harry spared the life of Peter Pettigrew, with consequences we have yet to see played out. Certainly Pettigrew's hesitant suggestions to Voldemort that they find an alternate victim for his rebirth spell came from Pettigrew's sense of life debt to Harry.

"Pettigrew owes his life to you. You have sent Voldemort a deputy who is in your debt...When one wizard saves another wizard's life, it creates a certain bond between them... and I'm much mistaken if Voldemort wants his servant in the debt of Harry Potter."
"I don't want a connection with Pettigrew!" said Harry. "He betrayed my parents!"
"This is magic at its deepest, its most impenetrable, Harry. But trust me... the time may come when you will be very glad you saved Pettigrew's life." (PA )

There is also ....Hermione, Ron, Ginny, Colin Creavy, Sirius(well he's dead right <_< ),Fleur,Gabreille,Justin Finch,Buckbeak,Mr. Weasley,....there may be more.

will any of this play a hand in book 7?