I love hearing anything by Adele and Annie Lennox. Annie has been singing since the 1980's, when she was the lead vocalist for The Eurythmics and I think she gets better as the years go by.
I like Patti Labelle and Chaka Khan. They have really strong voices and are bless to have that. Singing is singing outside of the studio and performing on stage giving it your all. I heard that from these artists.