Well as I said, avoid the English dub of
Grave of the Fireflies at all costs. I cannot stress that enough.
As for non
Ghibli, I have many, but my favourites would have to be
Akira and
Ninja Scroll.
It's hard not to acknowledge thouse films, as they both pioneering examples of the Manga genre, and two of the the first adult-themed feature lengths I ever saw. Both have outstanding animation, especially
Akira. The 2-disc DVD set with the remastered film along with a brand new English audio track is stunning.
Be careful to not come across the original non-remastered version of the film first, if you haven't seen it, because it was released on a standalone DVD. The picture is merely a little better than VHS, and the original English dub was always really confusing, which is why they recorded a new one and brought the dialogue into line with the original script, which was a huge improvement, and really quite good.