Thanks to DMW, Jana and Pecker - I'm hooked on Carnivale. I rented the DVDs from Netflix out of curiousity and it's now like a drug and I'm waiting for my next hit.

Also, after a little research, I found that HBO definitely only produced 2 seasons. They felt that the end of Season 2 tied up the story pretty well and didn't think a 3rd season was necessary. I can't find a release date for Season 2 yet.