Romeo x Juliet -- First episode, there's a ball.
School days -- When Sekai and Makoto dance at a festival.
Yogurting game -- Need I say more?
Vampire Knight -- End of the first season, I believe? At a ball.
Mahoromatic -- Ending
Hack Sign -- not sure where, but I knew there's a scene of them dancing =/
Macross Frontier -- from what i've seen
Popotan Game -- opening
Potemayo -- Just...everywhere.
Cardcaptor Sakura -- second movie