Sen to Chihiro no Kamikakushi, Gake no Ue no Ponyo Recommendations
Same director. Both are visually stunning and have a distinct Gibli, magical quality to them.
Ponyo and Spirited away are very similiar when it comes to the overall feeling. Its very cute and mysterious. And you really love the maincharacters in both. While Spirited Away is a bit more serious both are very lighthearted anime movies. Also Studio Ghibli made both.