Number one singles that have been (almost) completely forgotten

Nope, it was covered on the "Sing" soundtrack. It's part of the tryouts montage. Somebody must remember.

 

I am in a discoteque just now and the Shaggy single Oh Carolina came on, I had forgotten all about it... ,

 

Off the top of my head (U.S. Billboard number ones):

The Streak (Ray Stevens)
Seasons in the Sun (Terry Jacks)
Dark Lady (Cher)
Island Girl (Elton John)
[skipping past the obvious disco choices...]

It's Still Rock n Roll to Me (Billy Joel)
Stars on 45 Beatles Medley (Stars on 45)
Mickey (Toni Basil)
Rock Me Amadeus (Falco)
Seasons Change (Expose)
Because I Love You (Stevie B.)
One More Try (Timmy T.)

 

#1 in the UK, 1968

 

I still hear this one.

 

Maybe in the UK, but Denver was huge in the States in the mid '70s. Several number ones including Sunshine on My Shoulders, Calypso, and a live version of Thank God I'm a Country Boy (along with the aforementioned Annie's Song).

He was underrated as an actor too. Check out his understated performance in "Oh God."

 

Indeed, "It's Still Rock 'n' Roll to Me" remains overplayed to this day.

 

Amazing Grace-Royal Scott's Dragoon Gaurds

 

Featured prominently in 1995's Braveheart. Can't exactly fit it onto today's extremely limited oldies playlists.

 

And "Mickey" was on the radio just now.

 

I looked to see how many people had watched these songs on Youtube, roughly adding up various uploads (so long as it was by the original performer - live versions counted too). As you can see, some are very much better remembered than others, at least among Youtube users.

The Streak (Ray Stevens) - ~10 million
Seasons in the Sun (Terry Jacks) - ~7.5 million (Westlife cover ~44 mil)
Dark Lady (Cher) - ~900,000
Island Girl (Elton John) - ~900,000
It's Still Rock n Roll to Me (Billy Joel) - ~13 million
Stars on 45 Beatles Medley (Stars on 45) - too difficult to determine
Mickey (Toni Basil) - ~32 million
Rock Me Amadeus (Falco) - ~46 million
Seasons Change (Expose) - 1.6 million
Because I Love You (Stevie B.) - ~11 million
One More Try (Timmy T.) - ~4.5 million