Steve Winwood and Peter Gabriel.
The singer from Audioslave sounds just like that Soundgarden dude.
what? Oh. yeah. I knew that.
The cult singer/songwriter/musician Happy Rhodes has a high voice that sounds exactly like Kate Bush’s high voice. Their low voices are nothing alike though.
Amy Grant can sound exactly like Grace Slick.
Bonnie Tyler has sadly been forced to cancel her Christmas Tour as she hasn’t caught a cold.
Anastacia and Alanis Morisette are quite similar in style (at least to my hears, I can´t stand either of them).
David Hidalgo (los lobos) and Steve Winwood
Pete Drooge and Pete Yorn
There are times when Bill Medley has sounded very much like Ray Charles. Like on Georgia on My Mind, for instance.