Me. A must.
Mike Mearls. Knows what D&D is
about, and can write to it. (I don't think I have to spell out what he has done)
Barsoomcore. Because he thinks up some cool stuff. (Hot Pursuit. And barsoom, of course!)
Michelle Lyons. (Slayers d20, Races of Stone.) (As a side note, did anyone else get avatar brain lock and think that was sniffles up there asking why she was unloved...)
Mike Johnstone. Developer at SS&S. A good editor and a good developer.
Robert Schwalb. Another unsung, great designer. (Developed about a dozen green ronin and goodman products, and wrote a lot of great supplements like Aasimar & Tiefling and Unholy Warriors/Book of Fiends)
Bruce Cordell. He's been through the fire.
Someone in junior high right now. Just to emphasize I don't want to see this for a while.
With my list, I felt like you need more than authorial experience. Developers and editors are instrumental, I think, in ensuring that the game line comes together.