For me, the original Star Trek is the science-fiction equivalent of the Beatles and William Shatner and Leonard Nimoy are the Lennon/McCartney of the franchise. (Does that Make DeForest Kelley the Enterprise's George Harrison?) Leonard Nimoy's passing has reminded me just how much Trek has meant to me since I first encountered it (in glorious black and white. We didn't make the jump to a color set for a few more years) during its original run and what an incredible impact it's had on so many lives.
Of course Nimoy was far more than a pointy-eared Vulcan. He performed a wide variety of roles over the years: I remember seeing him on Broadway, back in the 70's, playing Doctor Dysart in Equus and, more recently, being delighted by his appearances on Fringe as the mysterious William Bell. Nimoy was also a poet, a photographer, a political activist, patron of the arts and, by most accounts, a man of heart and integrity.
The internet is filled with tributes but (for me, at least) there's nothing anyone can say that would be more heartfelt and eloquent than Doctor McCoy's words—written, I suspect, by the great Nicholas Meyer—at the end of Star Trek II: The Wrath of Khan: "He's not really dead as long as we remember him."
Heartfelt condolences to Leonard Nimoy's friends and family.