Cos I'm not the most in-depth comic fan in the world, a lot of these are just for a single, awesome pice of work.
Alan Moore - For lots of stuff, including Watchmen (which I don't enjoy reading as much as some others, but I have to respect the attention to detail)
Kurt Busiek - For Marvels (just cos of how all the pictures in it are from real comics, and the way it all fits together, quite astounding)
Mark Millar - For The Ultimates (I've never enjoyed six issues of a comic book more than the first 6 of this, and the next 3 arcs rocked pretty harshly too)
Garth Ennis - For the genre defying epic that is Preacher
Frank Miller - For Sin City (man, I wish I could be in one of those films, just to say some of that hard-boiled dialogue)
Not the most adventurous picks, but whatever, I enjoy and respect their work more than any others.