My mom loves her some Chaka. She went to a Chaka Khan concert back in the 80s and still has the pictures. By the looks of it and the stories I heard Chaka could put on a show! I like her well enough too along with the other "scream queens" - Aretha, Tina (fav), and Patti. Chaka is one of the few people I will agree covered a Prince song better than the original ("I Feel For You"). TLC also did a good job on "If I Was Your Girlfriend" from their CrazySexyCool album.
Speaking of covers, Beyonce does a cover of Anita Baker's "Sweet Love" in a medley of her own songs here: