From "Time for Lightspeed", seeing several ordinary but service oriented people rising to help as soon as they realize people need help. And the fact that this was the first ranger series with no Secret Identity. Seeing these new heroes rising up and being recognized as true heroes in and out of uniform is a new but sweet territory that Power Rangers moved into with this season.
The part in "Ocean Blue" when Chad and Marina press their hands against the glass a la the hand touch scene in Tarzan.
The end of "The Chosen Path," where Chad's old sensei finally accepts Chad's decision to become a Power Ranger and gets a tour of the Aquabase.
Seeing Dana and Captain Mitchell celebrating Ryan's birthday in "From Deep in the Shadows" after so many years, in spite of him being supposedly dead.
What finally restores Carter's memory during "The Last Ranger?" Seeing Dana's face as she tries to battle the monster-of-the week by herself. Not only that the memories that were shown were ones that he spend times with her.