Here's what I've seen already:
Mazinkaiser
Getter Robo Armageddon
Shin Getter Robo
Getter Robo Arc
Gunbuster
Diebuster
Gundam 0079
Zeta Gundam
Gundam 0080
Gundam Stardust memory
Gundam 08th ms team
Gundam SEED and SEED Destiny
Gundam 00
Mobile Fighter G Gundam
Gungrave
Trigun
Trigun Stampede
Code Geass
Evangelion
FLCL
TTGL
Akira
Ghost in the Shell
Ghost in the Shell SAC 1 and 2
Lupin the 3rd: The Mystery of Mamo
Captain Harlock SSX
Devilman Crybaby
Space Battleship Yamato 2199
Parts of Yamato 2202 and Gundam IBO but I never really got into either of those

What should I watch next?