Mouseferatu
Hero
Ann McCaffery, Dragonriders of Pern series. Tends to write the same book, over and over, whether it's Pern, Freedom, brainships, Acorna. That said, I still enjoy the first Dragonriders books, especially the Harper Hall series.
I was going to say something very similar about David Eddings.
I love most of Eddings' stuff. (I can say that because his series "The Dreamers" does not exist in any reality I choose to acknowledge.) I've read his other series multiple times since I was a teenager, and the Elenium is still one of my favorite fantasy trilogies. He's just such a fun read.
But holy crap, the man had exactly one plotline and one well of characters. The plots of The Belgariad, the Malorian, the Elenium, and the Tamuli are all pretty much the same. And the characters are all combinations of the same pool of personalities (albeit mixed and matched a bit differently).