There are loads of books which have stayed with me. Plenty of children's books - Blyton the Dark is Rising, Narnia, Just So Stories, Laura Ingalls Wilder, KM Peyton, Biggles, Tolkien. An anthology called I Like This Poem, also a Child's Garden of Verses. Then Pratchett & Gaiman's Good Omens. Douglas Adams. Alexander Cordell - the Fire People. Browning's Pied Piper of Hamelin, but it has to be the copy my grandmother wrote out for me and illustrated on every page in watercolours.
Also, we had a couple of slim books by R Meurig Evans - Children Down The Mines, which was extracts of interviews to the Royal Commission that led to the 1842 Mines Act. Those books and Cordell are a strong reason why I ended up with a history degree that included a dissertation on 19th century industrial and social Welsh history.
We passed a tattered copy of Lace round at school, and Flowers in the Attic. But it was Judy Blume's Forever which the headmaster confiscated from us in the playground.
I read a book called We Were Young and At War, which is a collection of teenagers diaries from WW2, from all round the world. The one which haunts me most is of a boy in Leningrad, who starts off all positive, going to the People's Palace and having fun with his friends, then all those things stop and it's more about finding food, because of the Seige of Leningrad - eventually his mother and sister are evacuated, but he is too weak to walk, and his mother is too weak to carry both children, so he's left alone in the flat, and the diary ends up tailing off because he dies of starvation, all alone this poor boy who had been so full of life and hope at the beginning.