Femme, Kivala, Tackle, Marika, Nadeshiko... Wasn't there an in-show Female Agito with feminine curves and everything? It might have just been for a split second, but it was pretty hot.
As for male costumes... If I was going to seduce someone while dressed as a Kamen Rider, I'd have to go with perhaps any of the Hibiki Riders, Kiva, Kuuga (Mighty or Amazing Mighty), or Black. One of those would definitely do the trick.