My iPod just played "Since I Fell for You" from the Bob James/David Sanborn album Double Vision. I picked up this album a few months ago via iTunes, and just added it to my shuffle (which picks up between 800 and 1000 songs that I haven't listened to much or too recently), so I don't know if I've listened to the whole thing -- at least not since I'm sure my brother played it when I was in college. Unlike most of the tracks I've heard, this one had a vocalist. As I listened, I suddenly realized that I recognized the voice, and listened more carefully and then I found a name, Al Jarreau. A quick search through google and I located a site selling this on CD and listing the people involved, which confirmed that Al Jarreau was a vocalist on the album. I was right.
Of course, Al Jarreau has a fairly distinctive singing style, so he isn't the hardest vocalist to recognize.