Sorry, this is not manga, but I'd like to mention [*The Idolmaster*](http://en.wikipedia.org/wiki/The_Idolmaster).

[The original game of The Idolmaster](http://en.wikipedia.org/wiki/The_Idolmaster#Game_series) is an arcade game about producing girls as idols.

However, the first anime series [Idolmaster: Xenoglossia](http://en.wikipedia.org/wiki/Idolmaster:_Xenoglossia) is a robot anime. Girls ride big robots named "IDOL".