Good point, Memories has that wonderful space sequence that Kon directed.
If you'd like to check out other unusual Japanese animation flicks with a more mature feel you can still check out a couple of Ghibli flicks like Pompoko, and Grave of the Fireflies.
Have you seen Jin-Roh? Very dark set in a world where the Nazis never lost world war 2.
Let's go "hard-to-find"
Also a very trippy and difficult to find video would be Night on the Galactic Railroad. Angel's Egg and 1001 nights are both by Yoshitaka Amano (Final Fantasy video game's character designer)
Finally - there's a new French animated film that I have to see. It's called Persepolis:
http://en.wikipedia.org/wiki/Persepolis_(film)
http://www.sonyclassics.com/persepolis/