Obvious choice, probably, but Morrissey (and his band The Smiths) probably did more for me during my adolescence than anyone else.
His wonderful lyrics - turning tales about lost and unrequited love ('I Know It's Over', 'Never Had No One Ever' etc) - into an endlessly quotable art form gets my vote.
Made some good friends back then through him. I figured, "If this person likes Morrissey, then we'll get along fine!"
Good to see Amelie featured here, by the way. Great movie!