i know kame,yamapi,aragaki sings some songs but who else

Tamaki Hiroshi - Fukuyama Masaharu - Sato Takeru
@panda yes KimuTaku sings (SMAPP)
Tamamori Yuta (Kis my ft2) 
actually pretty much all of Johnny's Idols
Ryo Nishikado from 1 Litre of Tears
Fuma Kikuchi from Toki wa Kakeru Shoujo
Almost every Johnny's (Arashi, Nagase Tomoya, Kimura Takuya, Kame, Yamapi, Ikuta Toma, Nishikido Ryo, Takizawa Hideaki, Doumoto Tsuyoshi, etc)
Fukuyama Masaharu
DAIGO
Kiritani Kenta
Hoshino Gen
Sorimachi Takashi
lately, Suda Masaki too.

Hirosue Ryoko started her celebrity career as an idol singer - she no longer sings now but she's the first Japanese artist I was really devoted to back in the 90s.

yamaP, arashi, hoshino gen, nissy, suda masaki...

Ok the list from MY stable of actors

Kamenashi Kazuya (Kat-tun)
Yamada Ryosuke (Hey!Say!Jump!)
Noda Yojiro (RADwimps)
ARASHI
  Matsumoto Jun
  Ninomiya Kazunari
  Sakurai Sho
  Aiba Masaki
  Ohno Satoshi
Yamashita Tomohisa (News and Solo..not made new music for 4-5 years now)
Ikuta Toma (Started out as a singer before Johnny's picked him up)

--Just basically look up Johnnys.net..they can do everything

The actors from High & Low

Iwata Takanori - (Member of EXILE and J Soul Brothers)
Sato Taiki(EXILE)
Fujii Shuuka (FLOWER)
Akira(EXILE)
Takahiro (EXILE and Ace of Spades) m. to takei Emi
Tosaka Hiroomi (J Soul Brothers)
Kuroki Keiji (EXILE THE SECOND)
Elly (Sandaime J Soul Brothers)

There are more but I need to resume watching dramas...Have fun