Though not exactly a series in the traditional sense, I love Larry Niven’s Known Space stories.
David Brin’s Uplift series is great too - Sundiver, Startide Rising, The Uplift War, Brightness Reef, Heaven’s Reach, The Shores of Infinity…I hope more are coming.
I saw someone mentioned ‘When Gravity Fails’. I read that one, even played the old PC game, have not read any of the later ones though the setting was very intriguing.
I’m posting my vote for Ann Rice and the Vampire series–it does get better after the first book. Tolkien is also one of my favorites and (I’m adding this for son)… HARRY POTTER. He loves it!
/hijack/My favorite moment in the E.E.Smith ‘Lensman’ series is when they are searching a database of scientists that fills a whole planet, and they do it with a card reader. /end hijack/
…Mercedes Lackey’s Valdemar books, save for the last few.
I think she peaked in the period from By the Sword to the Storms trilogy. Her more recent stuff, particularly in collaboration with her husband, seems flimsier, less satisfying. But I can go back and read her earlier work over and over.
– Bob
Twenty years or so ago I’d have picked Heinlein’s Future History. Then I lived through the early years of it, and discovered it’s not science fiction – just novelizations of history that hadn’t happened yet. 
My own list would include the Mindkiller and Callahan series by Robinson, the Vorkosigan series by Bujold, the Darkover series (pseudo-SF fantasy) by Bradley, the Deryni and Adept series by Kurtz (fantasy but very well done), and the Thousand Worlds series by John Barnes. Niven’s pretty well done with the Known Space series at this point, but anything by him with or without Pournelle is good. The Pournelle future history (Falkenburg-Mote) is mixed, some great and some just OK.
Eve asked:
Just got the outline for it done last month. Awaiting plot developments; you know, with this sort of stuff, you need to strike when the iron is hot. I promise you a review copy; it’s a sure-fire deMille-type Major Motion Picture.
(Fred and Bosca – the Mormon books are not considered canonical (pun intended), kind of like the sequel to Don Quixote that some idiot brought out, forcing Cervantes to write his own to replace it.)
Badtz Maru said:
Apparently, it’s a maru thing of some sort.
That game (Circuit’s Edge) was great, considering when it came out. I’ll never forgive the guy I lent it too who never returned it . . .
–
“Business is business, and action is action.”
-I am big for Simon R Green’s Swords of Haven series with Hawk and Fisher. Husband and wife guards in the worst section of the city of Haven, the butthole of the low kingdom. The characters are great and they also patrol one of the greatest places of have ever heard of, The Street of the Gods, where dieties set up places of worship shoulder to shoulder and cause wierd stuff to the street in general to happen. It is hard to explain without actually reading it, other than to say, if anything can happen, it will happen there.
and
-The Dream Park series of Larry Niven and David Barnes. Wonderful tight drama surrounding the most played and most popular game in the world, the dream park games where virtuality and reality combine into one huge video game. The characters are amazing, and the stories are not the games themselves usually, but something going on behind the scenes.
I’m surprised no one has mentioned a couple of my favorite authors/series, namely:
Raymond E. Feist/Daughter of the Empire series
and…
Elizabeth Moon/The Deed of Paksenarrion (sp?)
Both excellent series.
I can’t believe I forgot Modesitt’s Recluce stories, and I have all of them!
Tim Powers has done some good modern-day Fisher King fantasy novels lately.
For some reason I really like Christopher Stasheff’s Warlock series.
What’s wrong with children’s books, if they are well done?
Despite the hype, which usually puts me off, I bought for myself, read, and greatly enjoyed the first two Harry Potter books, and I will get the rest as they come out in paperback. (I buy paperbacks to save money and space, so I can buy more books.)
Ooh, just thought of another one:
Leo Frankowski’s Cross Time Engineer series. Not for everybody, but a very good re-working of the “Connecticut Yankee in King Arthur’s Court” thing in 12th century Poland.
Although most people seem to like only the first few of Frank Herbert’s Dune Chronicles, I loved it the whole way through, including the last two, Heretics of Dune and Chapterhouse Dune. I loved reading about the consequences of what occured thousands of years before and how the society/universe changed and adapted. I’m less enthralled with the two follow-up books by Brain Herbert and Kevin Anderson. They’re prequels and intersting as an exercise in “Oh, is that how that came about?” but the characters never really come to life for me.
Larry Niven’s Known Space.
Robert Heinlein’s Future History. Hell, anything by RAH, whether it fits into a series or not.
Lois Bujold’s Vorkosigan Saga. I’ve yet to run across a sci-fi book with characters this rich that can suck you right into it, breathlessly following their ups and downs. Hell, there aren’t many non sci-fi authors who can write characters like this. I admire her attitude towards writing for her deeply flawed heroes and heroines, “That’s how you get up a plot. You take your character and you do the worst thing to him that you can think up for him.”
Oh, and E.E. Smith’s Lensmen series. It’s the ultimate example of Space Opera, and lots of fun.
Ahhh, books. Something I know.
I’ll have to seconed the Wild Cards books. They’re really good even if I did read them out of order.
Other than that,
This Place has no Atmosphere by Paula Danziger. It’s pretty good, though it’s not very deep. It’s good for quick relax-your-brain reading.
Dragon’s Milk by Susan Flecher. Girl has to save dragon’s from hunters. Better than it sounds.
Song of the Lioness series by Tamora Pierce. Very good. Starts off as genaric teenage fantasy, but gets a lot better by the end.
I don’t know if this counts, but, Archer’s Goon by Diana Wynne Jones is excellent. Alnog with anything else by her.
Anything by Alan Dean Foster. Or Craig Shaw Gardner. And Heinlein. And Andre Norton. Or SF written before the '70’s
The Coloured Fairy Books edited by Andrew Lang. A collection of fairy tale from everywhere.
His Dark Matrials by Phillp Pullman.
Dragons Winter by ?
The Firebringer by ?(I’ll look these up at the libary tommrow, if it’s open.)
That’s all I can think of. Most of it is juvinile fantasy, but that’s what I’m reading right now.
I can’t believe nobody has mentioned S.M. Stirling’s Nantucket trilogy. The three books, “Adrift in the Sea of Time,” “Against the Tide of Years,” and “On the Oceans of Eternity,” deal with the island of Nantucket mysteriously being sent back to 1250 b.c. and how contemporary Americans deal with the cultural and technological gaps between themselves and Bronze Age cultures. The bboks are exceelent action-adventure novels.
I also vote for David Brin’s “Uplift” series. He has come up with the most intersting alien species and worlds I’ve read about in a long time.
In fantasy, Terry Pratchett’s “Diskworld” series is brilliant satire as knowing of the foibles of human nature as anything by Wodehouse.
Dune is the only series I’ve read since the Hobbit books. The series format lends itself to weak second books, from what I can tell from reviews.