Idle.....
If you are desperate enough you can always resort to John Norman's "GOR".
All 33 volumes of it. Trust me it's a long read......
Love,
Liz
Ah, Gor. I remember reading a lot of those. I thought (and still think) that the first 5 - 6? Anyway, the books Ballantine published weren't too bad, except for the last of them, which was when the whole "we've got slave girls" went from a standard piece of fantasy setting to a major center-piece. Up until that point, it was your basic generic fantasy, with a slight scifi overlay, and wasn't a bad read. Past that point, nah.
Another good, longish (18 books, last time I checked) series is Sharon Lee & Steve Miller's Liaden Universe books.
Terry Pratchett - Diskworld
In the category of not-so-long series, I'd also recommend Timothy Zahn - Blackcollar and Cobra series
Vernor Vinge - especially the Zones of Thought trilogy
Ken McLeod - pretty much anything
Iain M Banks - the Culture novels. Banks & McLeod have a similar feel to their work that I really like, that I don't seem to find in American authors. Charles Stross has the same vibe in his Estachon duology (I was disappointed when I heard he'd said there probably wasn't going to be a third book in that series).
Charles Stross - The Merchant Families series, The Estachon and (my favorites) the Laundry series (spy thrillers filtered thought H P Lovecraft)
John Scalzi - Old Man's War (military scifi)
Older stuff, H Beam Piper comes to mind. Scalzi did a "reboot" of [i/]Little Fuzzy[/i] a couple years ago, titles
Fuzzy Nation