At the very end of the Southern Air Temple episode, when Aang, Katara, and Sokka are flying away and Aang looks back at his home, you can see two interesting shaped clouds next to the temple. If you look closely, you can see that one of the clouds is Avatar Roku's animal guide, (who we meet in Winter Solstice part 1) Next to it, you can see Avatar Roku himself.( Who we meet in Winter Solstice part 2) It's sort of like Roku is looking down on Aang from up above.