Library Journal’s readers’ advisory maven Neal Wyatt takes on Downton. Read her read- & watch-alikes here. While I am not an expert in RA, I am (fortunately or un-) one in British period drama. In addition to Neal’s picks, I recommend:
The Buccaneers (on Netflix Instant) - Based on an Edith Wharton novel about American heiresses in England, this miniseries is what I imagine Lady Cora was like (to a certain extent) before hooking up with the Earl.
The Forsyte Saga (also a good read-alike) - This one shares Downton’s production values; it’s a really beautifully filmed miniseries. There are plenty of sour marriages and doomed loves to please any Downton fan.
Agatha Christie’s Poirot (1st season on Netflix Instant) - I am personally a Poirot partisan, but if you like the Bates plot line in season 2, you’ll like Poirot. Seasons 8 through 12, especially, have the lush costumes and opulent settings of a Downton episode. You’ll also see some familiar faces: Hugh Bonneville (the Earl) is in “Murder on the Orient Express,” Elizabeth McGovern (Lady Cora) in “Appointment with Death,” Phyllis Logan (Mrs. Hughes) in “Sad Cypress.”
Atonement (also a good read-alike) - There’s war, cross-class love, library sex, and scandal. Prepare to cry.
I’ve mentioned Atonement and The Forsyte Saga above, but the first book that came to mind for me is Kazuo Ishiguro’s The Remains of the Day. Dutiful butlers, repressed inter-servant love, and more war. (This time with Nazis!) A beautiful, subtle, heartbreaking work. There’s also a movie version.