My favourites are nausicaa, mononoke, totoro and chihiro (in that order) but I also love whisper of the heart, castle in the sky, Arriety and When Marnie was here. I think all Miyazaki films are a must-see.The one that I liked less because I have seen only one time is Howl (and only in spanish not japanese subs), but it will fix when I watch it again. The old works are interesting but don't have the Ghibli-feeling of it, so are totally skipable.Have you seen Summer wars, Paprika, The Girl who leap in time or Wolf children?Also, here it is one short if you didn't see