My "must see" list is comprised of:
Berserk
Hajime no Ippo
Hikaru no Go
Kimi ga Nozomu Eien
Lain
======
Some other ones that are enjoyable and worth seeing:
Ghost in the Shell
Hellsing
Cowboy Bebop
Spirited Away
One Piece
Twelve Kingdoms (
http://reptilian.net/bt)
Get Backers
Read or Die TV
Fullmetal Alchemist
Peacemaker Kurogane
Naruto
Chrno Crusade
Ghost in the Shell: Stand Alone Complex
Kenshin movies/OVAs
Vampire Hunter D: Bloodlust
Lupin III
Prince of Tennis
FLCL