There is an excellent 7 book series out there called "Outlander" by Diana Gabledon. An 8th book is suppose to be released in 2012. Each book is approximately 1200 pages so they are long reads. But every book is awesome! I strongly recommend this series!
I love the Tony Hillerman series too!
Since you both like crime mysteries, check out the Guido Brunetti series by Donna Leon and the Adam Dalgliesh series by PD James:
Have you already read the classic Hercule Poirot mystery series by Agatha Christie?
You might also check out fictfact.com -- there you can select a genre and they'll provide a list of series within the genre, with a chronological list of all the books in each series. You can set up your own lists and track the books you've read. They will also e-mail you when a new book is published in any of the series you're following. Sure helps me keep track of where I am in the series and what to look for next at the library.