The British Film Institute did make a list of the top films that they thought children under 14 should see (which isn't exactly the same thing as Family Films) - here are some of the ones from their list, plus some of those which my kids and I would regard as family films:
Beauty and the Beast
Pocahontas
Mulan
Lilo & Stitch
The Lion King
(older Disney's generally)
Back to the Future
Who Framed Roger Rabbit?
An American Tale
E.T.
Finding Nemo
Ratatouille
It's a Wonderful Life
Jason and the Argonauts (the old Harryhausen one)
King Kong (the old 1933 one, or the Peter Jackson one)
My Neighbour Totoro
Kiki's Delivery Service
Spirited Away
Ponyo
and all other Studio Ghibli films, with the possible exception of PomPoko and Grave of the Fireflies)
The Princess Bride
Willow
The Never Ending Story
Raiders of the Lost Ark/Temple of Doom/Holy Grail
The Railway Children
The Secret Garden
A Little Princess
To Kill a Mockingbird
Toy Story
Whistle Down the Wind
The Wizard of Oz
The Sound of Music, My Fair Lady, Fiddler on the Roof, Calamity Jane, Chitty Chitty Bang Bang, Meet Me in St Louis, Oliver!
Muppet Christmas Carol
Miracle on 34th Street
Little Women
Charlie & the Choc Factory
Both Nanny McPhee films
Peter Pan
Labyrinth
The Narnia films
The Grinch
High School Musical
Chicken Run
Ice Age series
Joseph & the Amazing Technicolour (Donny Osmond version)
Mary Poppins
Stuart Little films
The Jungle Book (Jason Scott Lee live version)
101 Dalmations (Glenn Close live version)
Wallace & Gromit & Curse of the Wererabbit
These are for the under-8/9 yr olds. Older family films would be Harry Potters, Jurassic Parks, Robin Hood Prince of Thieves, Waterworld, The Shadow/The Saint, or other musicals.