Well, I like Mercedes Lackey, especially her Heralds of Valdemar series. But she's good in general for fantasy.
I don't know if you've read Anne McCaffrey, but she's really good too.
Neil Gaiman's Neverwhere is excellent, but it's not a series. If you need to have a series, he's got a series of graphic novels called "The Sandman" that are also magnificent.
Terry Pratchett has a good sense of absurdity and sarcasm. He doesn't write in a series, really, but all the books he writes are written about one world, Discworld, and some characters are recurring.
If you're young-ish (or have a young soul) Tamora Pierce is a very good author. Everything by her is excellent, though it tends to be aimed towards the YA group.
If you're ... above the age of consent, shall we say, Anne Bishop's Black Jewels trilogy is good.