So I've read a lot of series of books this past year, and I felt like sharing some of them since I felt they deserved to be shared around! Here are a few:
Blood Ninja by Nick Lake
Evil Genius Trilogy by Catherine Jinks
The Secrets of the Immortal Nicholas Flamel by Michael Scott
Gone by Michael Grant
BZRK by Michael Grant
The Messenger of Fear by Michael Grant
The Mortal Instruments Series by Cassandra Clare
Keys to the Kingdom by Garth Nix
The Keepers by Lian Tanner
Finishing School Series by Gail Carriger
Pinball series by Murakami
A Tale of Fontania (I recommend the travelling restaurant and the queen and the nobody boy) by Barbara Else
The Seventh Tower by Garth Nix
The Lunar Chronicles by Marissa Meyer
Dorothy must die by Danielle Paige
Sabriel by Garth Nix
Dancing Jax by Robin Jarvis

And here are a few classic series:
Hunger Games by Suzanne Collins
The Chronicles of Narnia by Lewis Caroll
The Rangers Apprentice by John Flanagan
Percy Jackson by Rick Riordan
Diary of a Wimpy Kid by Jeff Kinne
Harry Potter by J.K Rowling
The Series of Unfortunate Events by Lemony Snicket

I hope I have shared some good reads, and anyone's welcome to add more!

Awesome! I've also read Garth Nix's series, and really enjoyed them. You are the first person I've 'met' that has also read Ranger's Apprentice, which is my personal favorite book series :) Have you read the spinoff Brotherband Chronicles?

One good series of books that I would recommend to people would be the Xanth series of books by Piers Anthony

Great adventure/fantasy series: Beyonders by Brandon Mull. He has several other good series as well

@Royalton, I'm really pleased I have 'met' someone who has also read Garth Nix's series! And personally, I'm actually surprised that not that many people know the Rangers Apprentice. It's easily among the top of the series I have read because of the amazing writing and description and world building, and no, I have not read the Brotherband Chronicles, I will definitely check it out!