First off Spriggan fells kind of like a Michael Bay movie with all it's action and blood but I'm not saying it's a Michael Bay movie at all just fells like it. It has a good story to back it up and it's fun to view...but it's not one of the best, it's no Akira:D
I have seen very few, but I really enjoyed Princess Mononoke and Kiki's Delivery Service. Akira was hard to follow--perhaps I'm too slow. Also enjoyed Armitage and Ninja Scroll.
Actually, I rather liked Spirited Away. The Cowboy Bebop movie was okay, also. The translations with anime tend to stilt the dialogue too much, which hurts the experience. Alas, I am too lazy to learn Japanese.