For me, I have to name George Perez first, because his Wonder Woman, for me, was absolutely definitive. Diana has been in print for over 70 years, and as far as I'm concerned, she was presented definitively twice - by William Moulton Marston, and by George Perez. Bear in mind I'm praising Perez for his WRITING here.
Then there was Marv Wolfman, who, with Perez, gave us Crisis on Infinite Earths, the comic I bought more urgently than anything before or after, possibly the greatest DC comic book series ever published. As if that wasn't enough, Marv Wolfman, again with George Perez, gave us the New Teen Titans, the book that, as far as I'm concerned, Xed out the X-Men.
There was Neil Gaiman, whose Sandman changed my perspective forever as to what a comic book could be.
There was Terry Moore, who wrote (and drew) Strangers in Paradise, a comic I would never have bought, if all I had to go on was the synopsis of what it was about.
There was Fabian Nicieza, whose New Warriors run is one of the top super-hero comic book achievements of the 90s.
There was Christoper Priest, who, as Jim Owsley, gave us the King Conan comic, a book that was more expensive than others on the shelves, yet I bought it any way, because it was that good.
How about you?