Below you'll find a list of book series that I enjoy reading. The Anita Blake and Stephanie Plum books are keepers and books I know I'll re-read more than the two or three times I already have.

Cherry Adair - I'm fond of both the Wright series and TFLAC series books. She combines romance and suspense very well.
Patricia Cornwell's Kay Scarpetta series (not as fond of the Judy Hammer series)
Janet Evanovich's Stephanie Plum series
Christine Feehan's Carpathian series (I also enjoy her leopard people, Ghost Walker and Drake Sisters series)
Joanne Fluke's Hannah Swensen mystery series
Sue Grafton's Kinsey Malhone series
Laurell K. Hamilton's Anita Blake series (not really fond of the Merry Gentry series)
Steven Hamilton's Alex McKnight series
Victoria Houston's Loon Lake Fishing Mystery series
Sherrilyn Kenyon's Dark Hunter series is a new discovery of mine and I'm enjoying the world she's created immensely
William Kent Krueger's Cork O'Connor series (though my favorite is his stand alone)
James Patterson's Alex Cross series
Kathy Reichs' Temperance Brennan series
J.D. Robb's Eve Dallasseries
J.K. Rowling's Harry Potter series
John Sandford's Prey series

I'd be lax in mentioning authors I love to read and are auto-buy's to me:
Stephen King
John Grisham
Thomas Harris
John T. Lescroart
P.T. Deutermann
There are many more, I know I'm forgetting some.