For the sad sacks who don't know him, he is one of the big names in F/SF, and one of the remarkably few who wrote both for print and for the screen (that classic ST:TOS episode, "The City on the Edge of Forever" was his, as was I Have No Mouth, and I Must Scream). He was also the editor of the groundbreaking Dangerous Visions anthology.
All of which is a prelude to a recommendation: I think Ellison did his best work as an essayist and film critic. He managed to infuse every article with his personal voice. He's a member of the Hunter S. Thompson School of Gonzo Nonfiction, and so a precursor of the blogging revolution and a man to emulate. (In case you were wondering what Harlan had to do with a writer's blog.) So buy these books:
Stalking the Nightmare
The Harlan Ellison Hornbook
They ain't necessarily cheap, though.