A personal favorite of mine. Noriko Sakai "Guanbare" As you can see there's a long standing tradition of dressing idols up like clowns from space. Remember that the next time you feel like slapping the HP! stylist & wardrobe staff.
Onyanko Club "Sailor fuku wo Nugasanaide" check this video of Momosu performing the song.
The late Yukiko Okada "Little Princess" I absolutely love this video, I love how the wota do what they do. Classic.