Akira is the boss - brilliant, strange, beautiful... it's just ace.
Sky Blue - think it's S. Korean and mixes traditional animation with CGi, very long and melancholy in places but worth the watch, as it's a great story.
Cowboy Bee Bop: the movie - totally brilliant. Ace animation, really tight in terms of fluidity of movement, and it's got a good story too. Good soundtrack too, a must-see.
Venus Wars was one of my faves from the late 80s but it's like Hen's Teeth.... you can get it on VHS(!!) still or a US region DVD; there's no UK version apparently.
Cyber City Oedo 808 is brilliant. Very brutal - it's about three convicts employed to work as police - and a fair bit of foul language if I remeber rightly, but it's from that era (late 80s/early 90s) when Managa and Anime was going through a boom.
Ghost In The Shell needs no introduction - wired, adult but worth watching.
Macross Plus - pretty good, lots of mecha
Lots of others that animated films that cross all sorts of genres:
Castle Of Cagliostro
Naussica: valley of the wind
Laputa - castle in the sky
Princess Mononoke - absolutely amazing, probably my fave Ghibli film
My neighbour Totoro
Ponyo
Arrietty
Spririted away
Howl's moving castle
Grave of the fireflies - awfully sad film about children during the war in japan.
Only yesterday
Kiki's delivery service
The cat returns
Bloodrayne
Blood
Perfect Blue
An of course you have the Urotsokudoji series, possible some of the weirdest cinema you'll find in animated form. Lots of hard-to-stomach stuff with plenty of demons doing the dirty with scantily-clad schoolgirls. It's not one to watch with anyone who's easily offended, especially by sexual content that is very, very out-there. The final film was deemed so bad by the BBFC that when you buy the DVD, you get the audio track hut with stills over the top as opposed to the animations.