All these posts, and no one’s mentioned Billy Joel and Ray Charles singing “Baby Grand,” off of Joel’s The Bridge album?
Aha! That was what I couldn’t remember earlier - does the Clapton/King album “Riding with the King” count?
Carm6773, I guess I’m a country music geek, too.
So, I’ll be the first to mention Alan Jackson and George Jones remake of “A Good Year for the Roses.” (from 1994)
The best duet IMHO is Bob Dylan and Johnny Cash doing “Girl from the North Country”
“When The Sun Goes Down” Kenny Chesney and Uncle Kracker
Garth performed this during the concert in Central Park but I don’t remember if Billy Joel was out on stage singing with him at that point or not. Don McLean also came out to sing “American Pie” and I’m sure Garth joined in. 
Throughout its existence, Chicago usually has been staffed by at least three lead singers (all male), so several of the group’s hits include voices by multiple male voices. But Cetera’s voice is the only one that, to me, is distinctive enough to pick out. I have never been able to tell whether the other voices are Robert Lamm or Terry Kath or Bill Champlin or whoever. So I couldn’t say whether any particular song was a duet or a trio or whatever.
I believe “Saturday in the Park” has multiple lead singers.
Terry Kath accidentally killed himself in 1977 or so and the multi-voiced Chicago hit that sticks out most in my mind is “Hard Habit to Break,” which was from the 1980s, so it couldn’t have been Cetera and Kath on that one, anyway.
The all time best selling female duet song is “I Know Him So Well” by Barbara Dickson & Elaine Paige from the concept album of “Chess.”
Bono and B.B. King, “When Love Comes To Town.”
I think it was Trent Reznor, not Marilyn Manson.
Hear hear! I was thinking of that song as soon as I read the title.
Of course that line’s funny because of the preceding lyric –
I would buy you a fur coat,
But not a real fur coat; that’s cruel.
When I was little, I had a Whitney Houston tape (yes, I know!), and one song was a duet with her mother, Cissy Houston.
Didn’t Chad Kroeger from Nickleback and Josie Scott from Saliva record a song together for the Daredevil movie?
Yeah, it was called “Hero.”
Bing Crosby and Johnny Mercer do a fantastic duet of “Mr. Meadowlark”
David Bowie and Billy Joel, Pressure.
Are you thinking of “Under Pressure” by David Bowie and Queen?
The baseline of which, essentially, became Vanilla Ice’s “Ice Ice Baby.”
Probably. I think I got so excited at finally coming up with something that someone else hadn’t already mentioned, I got carried away. 
OTOH, I’m certain there was a duet Billy Joel did with another male, on a CD of his I had. Hmmm. Well, not worth losing sleep over, I guess.
Billy did a song called Pressure, which can be found on the Greatest Hits I & II CD (I don’t remember which CD it was on originally, and like norinew, I don’t want to look it up). It was not a duet, though.