1) Callahan's Con- Spider Robinson. It's actually last in the Callahan series, but it had just come out when I first read it and then it became a frantic process to own all other books. Callahan's series made 12 year old me's opinions about prostitution change completely, and also introduced me to the concept of polyamory.
2) Harry Potter- thanks for giving me fandom, which is a good 70% of my enjoyment of life.
3) Slot Machine (and) Extreme Elvin- Chris Lynch. Read SM for the first time in 7th grade. These books basically set up my whole sense of humor. Over a decade later, with chapters memorised, they still make me laugh out loud in public places when I read them. PLUS HOLY FUCK BALLS THERE'S A 3rd THAT I NEVER KNEW ABOUT UNTIL A MONTH AGO BUT COCONUT_ICE22 BOUGHT IT FOR ME FOR XMAS.
4) Savages- Don Winslow. I love it for the poly, and I love it for the drug use, but most of all I love it for the style. I'm not generally one for literary works of art, and I still wince thinking of HP's litfic wank era. That being said, I love a book with STYLE. Clockwork Orange, Trainspotting, Pygmy, anything with it's own language really gets me. And Savages has that in spades.
5) NeverNever (and the rest of the Bordertown series)- Will Shetterly (and assorted). My first urban fantasy book as a kid. I lost track of the name/author, could only remember the cover and the concept. Then I found it again, and I love it as much I did at 10.
6) Yes Man- Danny Wallace. They made a movie based on it, but the book is far funnier. And by far I mean the first time I read it my dad got really angry at me and told me I had to read it when he wasn't home because I was laughing at every paragraph and I'd been reading for an hour and IF YOU DON'T SHUT UP I'LL MURDER YOU.
7) Archer's Goon- Diana Wynne Jones. I have never wished harder for anything to be a movie ever. It was the first book of her's I'd ever read, and thank god for that, because she's an entire shelf these days. I HAVE A LOT OF FEELINGS ABOUT TORQUIL, OKAY?
8) Mindhunter: Inside the FBI's Elite Serial Crime Unit- John E Douglas. When I was a little kid (like 5 and up) and I wanted to spend time with my dad after his nap but before dinner, I'd crawl into my parents bed and he'd read out chapters of the profiling and case study books he was reading. Since I met my girlfriend partially through our shared love of serial killers, I thank my dad for nurturing this interest.
9) Anything Macdonald Hall- Gordon Korman. Well DUH. It's only been my most read series since age 7. I only started signing up for Yuletide because there's a tiny MH fandom during Yuletide. Codependant BFFs, crazy schemes, and women that could put your ass through a blender without a electrical socket- what's not to love?
10) I don't know I can't think of a 10, but John Scalzi and Cory Doctorow are both great authors that are pro-fan culture, so there's that.