#13 Justice League : The Savage Time
The true measure of a hero shouldn't be his powers, but how he acts without them. In the Justice League episode, The Savage Time, John Stewart and company go back in time to prevent meddling that allowed the Axis powers to win WWII. During the course of events, the green lantern ring ran out of juice.
Lack of powers wouldn't stop the ex-Marine from keeping on fighting. John joined up with Sergeant Rock's Easy Company where he continued to play a critical role in defeating Vandal Savage's army.
#25 - Justice League Unlimited: Initiation - John Stewart's new look
#24 - Batman: The Brave and the Bold: Death Race to Oblivion! - Guy Gardner's Lanternmobile
#23 - Justice League of America: Pilot - Doesn't air
#22 - Justice League Unlimited: The Once and Future Thing: Time Warped - Hal Jordan joins the league
#21 - Legends of the Superheroes - Lantern goes live-action
#20 - Justice League: Crisis on Two Earths - Darker shade of green
#19 - Batman Beyond: The Call - Lantern of the future
#18 - Static Shock: Fallen Hero - Hero Worshiped
#17 - Batman: The Brave and the Bold: The Revenge of the Reach! - Loads of Lanterns
#16 - The Batman: Ring Toss - Gotham by Greenlight
#15 - Justice League: Hearts and Minds - More to the Corps
#14 - Justice League Unlimited: The Return - The Corps is Greener Yet
#13 - Justice League: The Savage Time - Ringless