The Janie Johnson Series by Caroline B. Cooney
It all started with The Face on the Milk Carton. Janie finds a milk carton with her own face on it and realizes that nothing about her life is true. She is determined to find out exactly what happened when she was little, but the truth isn't revealed after just one book — you quickly followed up in Whatever Happened to Janie, The Voice on the Radio, and What Janie Found. These books were your introduction to thrillers and mysteries, and nothing can replace that!
The Uglies Series by Scott Westerfeld
Imagine a world where looking normal is a bad thing. Not just bad: Ugly. These people are considered Uglies until they make the transformation into Pretties, something all teenagers looked forward to eagerly. This was the perfect middle school and early high school read, when everyone was in the "awkward phase" and waiting for real life to really begin. This one followed up with Pretties, Specials, and Extras.
The It Girl Series by Cecily von Ziegesar
If you grew up loving Gossip Girl throughout your middle and high school years, chances are, you were ecstatic about the follow up It Girl series by the same author. Set in a boarding school but following similarly wealthy, often catty girls each desperate to be the It Girl of the school. Best of all? At the heart of this series was Little Jenny Humphrey from Gossip Girl, who kept everything interesting.
The Internet Girls Series by Lauren Myracle
Before emojis, and before iPhones, there was the Internet Girls series. This one was perfect for anyone who grew up in the AIM era, as it was written fully in instant messages and emails. Follow up with TTFN, L8R, G8R, and finally, in 2014, YOLO.
The Clique Series by Lisi Harrison
Gossip Girl but for younger readers. The Clique was a group of young girls, whose parents did basically whatever they wanted, who wore whatever they wanted, and who walked around their exclusive school like they own it — which they probably did. This series was filled with varying covers of posh plaid and punny titles, all of which were a big hit in the 2000s.
The Babysitter's Club by Ann M. Martin
I don't know if you could have forgotten these books, but just in case... a '90s classic if there ever were one. The Babysitter's Club all started with Kristy's Great Idea, and carried us into young adulthood wanting a group of friends like the BSC, not to mention, brought to life our inner entrepreneur. There are 131 Baby Sitter's Club books total, not to mention the spin-offs, and chances are, you read the majority of them back in the day!
The Private Series by Kate Brian
The stars of the Private Series were the Billings Girls, and if you were invited to join their infamous clique, you did everything you could to stay there. For Reed Brennan, the friendship of the Billings Girls was everything she ever wanted and more, but when she learns of the dark secrets within the group, the friendships among the girls begins to weaken. This was a personal favorite when I was younger, one that led me and probably many others straight to things like The Girl on the Train when we reached adulthood.
Artemis Fowl Series by Eoin Colfer
Like The Internet Girls series, Artemis Fowl only ended within the last few years — 2012 to be exact. The first installment, Artemis Fowl, was released in 2001, right in the middle of the Harry Potter craze. It fit right in with its fantasy elements and secret, hieroglyphic-esque language, and was an understandable New York Times bestseller.
The Sweet Valley High Series by Francine Pascal
Sweet Valley High goes all the way back to 1983, so chances are if it was revisited now, it would be a little dated. But that didn't deter young '90s and '00s readers from devouring all of the adventures of Elizabeth and Jessica Wakefield one by one growing up!
The A-List Series by Zoey Dean
The West Coast version of Gossip Girl was Zoey Dean's A-List Series. A group of girls: Anna, Camilla, Sam, and Dee take Beverly Hills by storm in this series, accompanied by their male counterparts, Adam and Ben. The sun is shining, the girls are beautiful, and Zoey Dean made you wish you were California Dreaming with each of the 10 installments of this teen series.
The Tillerman Cycle by Cynthia Voigt
The Tillerman Cycle was much darker than the rest of the series on this list. The Tillerman children are abandoned by their mentally ill mother, and are left to care for each other and find a new home on their own. There are seven books total in the series, all overlapping with each other, and drawing us in with each new installment of the Tillermans.
The Inheritance Cycle by Christopher Paolini
Another amazing magical follow up to Harry Potter, Eragon was the first in the Inheritance Cycle. Eragon, a young boy, finds a rock, and from that rock comes a dragon. Tell me you didn't want a dragon after this series and I will assume you are lying. There were three books after this one: Eldest, Brisingr, and finally, Inheritance.
The Gemma Doyle Series by Libba Bray
The Sisterhood of the Traveling Pants Series by Ann Brashares
Everyone seemed to read and love this book at once, and then the movie, and the rest of the series in a never ending surge of love for both Ann Brashares and their own friendships. The Sisterhood of the Traveling Pants started everything, but continued until only recently with the final installment: Sisterhood Everlasting. We grew up with Bridget, Tibby, Carmen and Lena, and they followed us into adulthood, too. Could it be more perfect? Probably not.
The Princess Diaries Series by Meg Cabot
Was I the only one who realized these books were a thing after falling in love with the movie? I couldn't have been more excited to realize the story continued! And is still continuing: Royal Wedding was just released this month!
The Confessions of Georgia Nicholson Series by Louise Rennison
This series always reminded me of Bridget Jones's Diary for YA readers. It's written in the same journal style, with Georgia Nicholson lamenting the ups and downs of being a teenager. The series has 10 books following the initial Angus, Thongs, and Full-Frontal Snogging, giving us an entire childhood spent with Georgia Nicholson and the many, hilarious things that happened as she grew up herself.