Grave of the Fireflies is really good, but I think it's the saddest movie I've ever seen, so I can't bring myself to watch it again.
Here's my own list (in no particular order):
My Neighbor Totoro
Kiki's Delivery Service
Porco Rosso
Whisper of the Heart
Ponyo
Arrietty
Finding Nemo
The Incredibles
Cars
Tin Toy
Jack-Jack Attack
BURN-E
Coraline
Tangled
Fantasia (1940)
Aladdin
Mulan
I might've forgotten how good some animated films are, though, so they were left off the list.