I belonged to the SFBC a long time ago (around the late 90's) when I lived in the US. It worked out pretty well but the only thing that I didn't like was the fact that most (all?) of the books they had available were hardback and I usually like paperbacks
Of course, the plus side was that I got some really good stuff from them like "The Compleat Dying Earth" by Jack Vance and "The Prydain Chronicles".
As for the authors you'd listed, I haven't read any Orson Scott Card or Robing Hobb myself but from what I know of them, I don't know if they have any books not in a series.
I do believe that Robin Hobb as Megan Lindholm (Robin Hobb is a pseudnonym as well
) might have a few stand-alone books but as Robin Hobb, she has 4 series of three books each so far.
OK, I did a lookup and Orson Scott Card does have some standalone novels but the most famous of his works - Ender, Alvin Maker, Shadows etc. - are all part of a series. Hope that helps