The songs DrSenteniel shared are Becoming Popular (at left), Giggle at the Ghosty, Winter Wrap Up, Hush Now, Quiet Now, and At the Gala. Each one of these videos is beautifully done and should help any pony fan interested in learning to play the songs on piano.
You can find the other four videos after the jump. There's also sheet music for DrSenteniel's version of Winter Wrap Up. You can check out DrSenteniel's Youtube channel.
An Important Edit: The sheet music for Winter Wrap Up was transcribed by sociomaladaptivist, who has a Youtube channel with lots of really great music!