If you have not seen:

Cowboy Bebop
Trigun
Berserk
FLCL (Fooly Cooly)
Mobile Suit Gundam (original movie trilogy)
Samurai X
RahXephon
Neon Genesis Evangelion
Tengen Toppa Gurren Lagann
Samurai Champloo

You owe it to yourself to do so, as an anime fan. The weakest on the list is probably Berserk, but that's because it was cheap and really is little more than a glorified introduction to the manga, which is up there on the list of the most epic ever put on paper. It's still got a fantastic cast of characters and an excellent, excellent plot and fantasy setting that make up for ty animation.