I personally prefer Takeuchi Mariya. Although Variety isn't my favorite album, Mearsy Beat, Amphitheater no yoru and Plastic Love are by far my favorite songs of her (not to mention she has one of the best english pronunciation I've ever heard on a japanese artist). Sweetest Music and Love Songs are definitely my favorite albums though, September being my favorite song there. There are other goods examples outside of disco though, Matsubara Miki is a good one.
Clio reminds me a bit of those weird electronic experiments so characteristic of Yellow Magic Orchesta while still maintaining that groovy base and sound.
This Yasuaki Shimizu has a slower tempo, I like it.
You definitively should check the first albums of Yamasaki Hako (Specially Tobimasu and Ningen Magai) and also some of Sai Yoshiko (ALL of her 70's albums, Mangekyou, Mikko and Taiji no Yume) if you want to feel the not-so-trendy side of japanese music. Sai Yoshiko in special is EXTREMELY underrated. I've been meaning to make a thread of this and provide translations for their songs but college has been eating my time. Hopefully I'll be able to build my computer this/next week and post it.