Okay, throwing some obvious big franchise answers (like Warrior Cats and That-One-I'm-Disappointed-In) aside, here's what I got at the top of my head:
Castaways of the Flying Dutchman (and the sequel) by Brian Jacques
Pirates! by Celia Rees
(which as I now remember included girls pretending to be men and joining a pirate crew to escape abusive society, no shit I liked it huh)
The Young Wizards series by Diana Dwane
Space Demons by Gillian Rubenstein
And The Great Ghost Rescue by Eva Ibbotson
There were, of course, also Varjak Paw, Molly Moon, Nina (by Moony Witcher, digging the name here), Children of the Lamp... I LOVED reading as a kid. Ask me if I've seen a movie and I'll probably say "No, but I've read that book!" x)