I'm finding that since I've started joining reading communities and experiencing independent authors, my idea of what is a must have author is undergoing changes. So I'll list a few that have been must haves for a while:
A A Attanasio
Iain M Banks
I haven't read all books from those authors yet, but it is fair to say that as soon as I see a new book release I'm planning a purchase.
However, I have to say that my interest in a wider range of authors is increasing and has increased quite drastically in the last few months thanks to communities such as MR. Thanks all.