The ending of "Tails' New Home", where both Tails and Sonic come to accept that Sonic is Tails' family, after searching for his parents. Their dialogue... just read it yourself.
Tails: "I've got a real family. I've got the best!"
Sonic: "Oh yeah, where?"
Tails: "A family is just people who care about each-other more then anyone else, right?"
Sonic: *gasps* "Right..."
Tails: "You're it! You're my mom, you're my dad and you're my picket fence!"
Sonic: "Woah! You're not gonna use the "L" word, are you?!"
Tails: *thoroughly embarassed* "Well..."
Sonic: *grabs Tails from behind and spins around* "Then I will, because it's a great word. I love you, little bro! Now I've got something even more important to say: "Noogie time"!"
Tails: *laughing* "It's good to be home!"