SRL isn't really a top ten bestseller, but he's a legend among the Celtic mythological authors. I'm not sure too many people would have ever even heard of him - if you haven't, and you like Celtic mythology and epic stories of overcoming the odds, check out his books. www.stephenlawhead.com/
Lawhead himself was once a professor of Celtic lore, studying for many years before becoming an author. His most successful series is the Pendragon Series - five books that tell, in great detail and elaboration, the story of King Arthur from a Celtic viewpoint. It's definately not your average Arthur story - the depth of detail and definition given to the characters is amazing. His first book in the series, Taliesin, doesn't even have Arthur in it - it's about the parents of Merlin (Myrddin) and how the Fair Folk came to the British Isles.
Anyway, I think he's a great author. My favorite series of his is the Song of Albion series; favorite book without a series is Byzantium. If you've ever heard of Lawhead, be you fan or critic, please post. I'd love to hear what other people like and disliked about his works.