1) Kirikou and the Sorceress
Visually stunning and well-written, this European film stunningly illustrates West African folk tales. You'll laugh, you'll cry, you'll be blown away by the incredible artwork. I really can't recommend Kirikou & the Sorceress enough. A midquel has recently been released and I can't wait to watch it!!
2) The Flight of Dragons
Made by the creators of the more popular animated Hobbit and The Last Unicorn movies, The Flight of Dragons is artistically wonderful. But the writing is unbearable, so watch this one on mute with some Jefferson Airplane or Led Zeppelin playing. This film is purely aesthetic.
Availability of this movie on DVD has been shaky, sadly.
3) The Secret of Kells
Another one that's absolutely amazing to watch, but the writing is just okay. The first 10 minutes of the movie aren't much either, so just skip ahead and turn on some Primus. Inspired by Celtic knotwork and medieval calligraphy, the artwork of this film never ceases to amaze.
4) Heavy Traffic
A Bakshi film clearly based on Eisner's Contract With God, this gives a gritty idea of life in NYC in the 70's. You'll be left feeling filthy and disturbed afterward, but grateful for the experience. It's unpleasant at best, raw and honest.
5) The Point
Created by musician Harry Nilsson (and narrated by Ringo Starr!), it was clearly the Schoolhouse Rock people who animated this trippy film. Nevertheless, this film of hippie-philosophy takes you down the rabbit hole where you can turn on, tune in, and drop out.
Honorable Mention: The Puppetoon Movie
Ok I can't not mention George Pal. A Hungarian claymation artist and producer who fled to LA to escape the Nazi regime, he revolutionized both his field and special effects overall. Yes, his films can be extremely racist - it's important to preserve that sour chapter of American history to see how far we have[n't] come.
Also, these were among the first music videos: Dutch-inspired claymation set to big band!