Ideon, created by Gundam creator Yoshiyuki Tomino, also check out the manga Mobile Suit vs Giant God: Gigantis' Counterattack which was a crossover between Gundam and Ideon
Golion, which was dubbed to make lion Voltron
Dairugger, made into Vehicle Voltron
Transformers Headmasters, Masterforce, Victory
The Macross franchise
Neon Genesis Evangelion
Gunbuster
Giant Robo the Animation is pretty good. At least until the last couple of parts.
You may have already seen them, but if you haven't, I would look into Macross and Macross Plus. It's not quite "giant robot" but both have good stories and mecha.