Some personal, off the beaten track favorite series':
Swallows and Amazons - Arthur Ransome (English schoolchildren, sailboats, camping, a classic)
Half-magic - Edward Eager (four children and lots of strange magical happenings)
Dealing with Dragons - Patricia C. Wrede (friendly dragons, rebellious princesses, long before "Shrek" found irony in fairy tales).
I have a lot more suggestions, but want to see what other people think!
Early readers (about age 7-8), Toys Go Out, My Father's Dragon, The Magic Tree House Series, The Weather Fairies series, The Rainbow Fairies series. For a little older, anything by Beverly Cleary and the non-fiction series, "Who Was..." "Who Was Amelia Earhart?" "Who Was King Tut?" I'm interested in more advice for a 7 year old who is reading beyond her years and by herself. She blows through Magic Tree House and The Weather Fairies asking for longer books and reading constantly. But it's challenging to find content that is not too life informing or frightening at the level that she's reading.