Grave of the Fireflies would definitely be there along with My Neighbour Totoro, Kiki's Delivery Service, End of Evangelion (but onlyfor those who've seen the series), well that's 4 already, there are far too many great ones.

Nausicaa valley of the Winds 
Akira
Ghost in the Shell
Spirited Away
Perfect Blue
Princess Mononoke

and more.

I haven't seen Howl's Moving Castle or Steamboy and if you notice, most of the ones I've listed haven't even been commented on yet. I am hoping that "A" will do a review or comment on Ghost in the Shell.

Cheers Trev.