From Halopedia, the Halo wiki
Grunt Minor • Grunt Major • Grunt Ultra • Grunt Heavy • Jackal Minor • Jackal Major • Jackal Sniper • Drone Minor • Drone Major • Brute Minor • Brute Major • Brute Ultra • Brute Captain (Captain Major • Captain Ultra) • Brute Jumppack • Brute Bodyguard • Brute Stalker • Brute Chieftain (War Chieftain) • Hunter • Infection Form • Elite Combat Form (Shielded) • Human Combat Form • Brute Combat Form • Carrier Form • Pure Form (Tank Form • Stalker Form • Ranged Form) • Sentinel Minor • Sentinel Major