One of my personal favorites. 
It’s been driving me crazy (literally–can we kidnap Koontz and make him finish it?) since I listened to Fear Nothing and Seize The Night…on cassette!
That got me hooked on audiobooks. The perfect voice (smoky, surferesque, wiseass-yet-mysterious) for an iconic character.
My current series? The “Chaos Walking” trilogy. Starting with The Knife of Never Letting Go.
I just finished John Scalzi’s Old Man’s War series. Really quite excellent despite the spartan writing.
Right now I’m working my way through the first book of Kim Harrison’s Rachel Morgan series. The friend who recommended it to me said it was a lot like the Dresden Files. …I gotta tell you, it ain’t no Dresden.
The series pretty consistently improves with each book, although there’s some controversy over 12 and 13, the latest two.
Does manga count? I’m working my way through the Death Note series. I finished book four, and I’m waiting on book five at the library. (Yes, book six came first, dammit.)
The Dresden Files, although I’ve lost steam (I’m somewhere around 2/3s in, and I’ve heard the last couple are interesting and different so I’m a little motivated)
Discworld
Song of Fire & Ice (trying Clash of Kings again; didn’t finish last time but the TV series reinvigorated me)
I also recently started the Millenium trilogy, but doubt I’ll get to #2 unless boredom truly overwhelms. Trying to focus on nonfiction a little more lately.
Questions, questions, Dung Beetle.
I’m still working on the last of Tolkien, with “The Children of Hurin” in the queue on my shelf.
I’m also working on the Border Trilogy of Cormac McCarthy, with “All the Pretty Horses” read and “The Crossing” to come next.
Many years ago, I lost interest in the Aubrey-Maturin Napoleanic War naval series, by Patrick O’Brian after about half a dozen books. I think I was reading them over too long a period, with other books interspersed between, losing the larger thread of the stories, but I’m not sure what caused this loss of interest in the series. Instinct says I’ll finish it up one day. I read C.S. Forester’s entire “Hornblower Saga” as a college freshman and loved it.
I conclude from reading all of these that it’s probably best to read a series one after another, usually without a break, unless fatigue with the story starts to cause your interest to flag. That’s not my usual habit.
Bonus: One of my friends, a former policeman, was crazy for the “Flashman” series, of George MacDonald Fraser, reading them over and over again and raving with delight about the character’s many faults and lucky fate. I suspect a psychological dimension here, something in a basic reaction formation.
Chalk me up as another inspired by A Game of Thrones (the HBO series) to read the series A Song of Ice and Fire (finished A Game of Thrones quickly and am about a quarter of the way through A Clash of Kings).
I’ve read Scalzi’s Old Man’s War and Butcher’s Storm Front and Fool Moon, but have not yet continued with those series (I fully intend to do so at some point).
Technically I’m not sure if it’s a series, but I’ve got the last of Christopher Moore’s vampire love story trilogy (Bite Me, which followed Bloodsucking Fiends and You Suck) waiting on my Kindle. Also, have been waiting for the conclusion to The Strain trilogy by Guillermo del Toro and Chuck Hogan, and I’ve just seen it’s going to be available October 25 (which is good news!).
I decided to read the A Song of Ice and Fire books before watching the HBO adaptation. I’m about two thirds of the way through A Clash of Kings.
Winston churchill “History of the English Speaking People”
Great series - re-read them every time a new one comes out - but you are correct some parts are boring - I just skip those chapters rather than the full book.
Stopped with a few more to go in The Dresden Files: Don’t want to burn through them too fast.
Received the latest ASOIF volume: Don’t feel up to hefting that weight right now.
Up to date on the Temeraire series: The books outside the Napoleonic War setting aren’t as much “fun” but the author is dealing with the larger picture of a world where Dragons Are Real & I’m still enjoying them.
Received the latest Mary Russell book yesterday (The God of the Hive): Just started reading…
Need to go through my Flashman books. Have I missed any?
Diskworld by Terry Pratchett - Long may the roll off the press
I have found that if I read several books in a row by a single author, then I start noticing the inevitable repeated phrases and other quirks in their writing. That’s why I’m in the middle of so many series - I need to swap between authors frequently.
The Dresden Files as they come out.
The Discworld Novels, but not much longer. 
I’ve just started A Song of Ice and Fire, and I’m afraid I’m going to have to make George RR Martin cry if he doesn’t start putting books out faster.
I’ve also been downloading the Barsoom series off Project Gutenberg to my iPod. I makes for great light reading for five or ten minute stretches when I’m waiting for children to fall asleep, or files to run, or I’m otherwise “indisposed.”
Simon Scarrow - the Eagle series… Very good - blood and guts about 2 roman soldiers - only criticism - it could be set in any army at any time in history (although I think he watched to many WW2 movies) based on the way Cato and Marco talk