Ten Favorite Book Series.
- The Bobbsey Twins series. The first series books I ever read.
- The Nancy Drew series. My introduction to mysteries.
- The Hardy Boys series. The logical next step after Nancy Drew.
- All Agatha Christie's Jane Marple books. I have read them all at least twice. I have read all the Poirot books, too, but the Miss Marple ones remain my faves.
- John Sandford's Prey series. Also his Virgil Flowers series and his Kidd series.
- The Kay Scarpetta books by Patricia Cornwell.
- The Parasol Protectorate.
- The Song of Ice and Fire series by George R.R. Martin. More popularly known as Game of Thrones. I started listening to the audiobooks back in 2005. After #4 they got way too complicated for me; I can no longer keep track of the characters. But the first three were riveting.
- Dorothy Sayers' Lord Peter Wimsey series. I want to be Harriet Vane when I grow up.
- The business-based series by Emma Lathen featuring John Putnam Thatcher. Perfect mysteries for an accountant reader.
…and then she voted.
kmkat & her kneedles 
I also LOVE Miss Marple and don’t know why I forgot her on my list. I’ve considered Game of Thrones many times, but I’m fairly sure they’d get too complicated for me way before #4. Off to vote…
Ahhh yes, Miss Marple!! I watch Game of Thrones but I feel like the books would be too complicated, as you said.
I haven’t read Emma Lathen, or all of the Sandford books, but otherwise my list would look remarkably like yours!
There’s also the Wheel of Time series, though I admit I haven’t read the last one. (Do I get bonus points for having read the first 9 of that series out loud? I was a living audiobook for the daughters, dontcha know.)
Did the Bobsey Twins have artwork in them? I seem to remember that. Twins and Tabiffa series did, and I don’t know if it was “Tabiffa’ or Tabitha. Great illustrations, I know. Nancy Drew was a big yes. Drive a convertible? Check. Plucky dark-haired sidekick? Check. Hidden secret latches and passageways? Check. Illustrations? Check. Also Hardy Boys, but more importantly Tom Swift! those were cool, all death-rays and stuff.
Peter Wimsey/Harriet Vane gets a big Hell Yes! I couldn’t abide the Swarm of Stords series. Hello, relatively small habitable environment and everybody goes nuts and burns out all the food suppliers and how long is your winter going to be? To say nothing of – nope, that’s enough wet blanket for me.
Parasol Protectorate looks good, I’ll check it out, thank you.
For me, The Red Mars series by Kim Stanley Robinson. Admittedly it’s only three books, but they Blew. Me. Away. Pretty much everything he writes is in the Blown Away category for me.