Mine has to be Purple Rain by Ruth Lorenzo
https://www.youtube.com/watch?v=i3o-HvS8LLI

Two off the top of my head:

JLS singing Umbrella

Luke's sing off with 'Run'

Edit to add Mary Byrne and 'It's A Mans world'

Eton Road and 'Does Your Mother Know'

Fleur East - uptown funk
Alexandra - listen
James Arthur - impossible

IMO

Leona Lewis - I Will Always Love You/ Somewhere Over The Rainbow/ All By Myself or A Moment Like This

Forgot to add Leona Lewis - Summertime

mine is anything from G4

4th Impact - Bang Bang
Janet Devlin - Fix You
James Arthur - Impossible
Alexandra Burke - Listen

Yes I agree , but Fleur East is a very close second with Uptown Funk

Andy Abrahams - Me And Mrs Jones
Robert Allen - Mr Bojangles
John Adelye - A Song For You
Rough Copy - Hit The Road Jack

off memory:

Diana Vickers - Man In The Mirror
Only The Young - Monster Mash
Misha B - Rolling in the Deep
Lauren Murray - One Last Time

It's nice to see someone has remembered John

I loved his voice and that song really suited him.

I've just remembered another two I liked - Rhydian doing Phantom and Joe doing Don't Stop Believing

Nikitta Angus - Bring It On Home
Alisha Bennett - Valerie
Diana Vickers - Yellow
Lauren Murray - One Last Time

How could we forget The Legend

https://www.youtube.com/watch?v=QWEp9p-ppfQ

https://www.youtube.com/watch?v=a2tNdp_G3dY

BiB -

https://www.youtube.com/watch?v=PQJVUhvg1kk

Matt Cardle - Baby One More Time, Knights in White Satin and his Bootcamp version of First Time Ever I Saw Your Face.

Yep, loved it as a performance I'm afraid. I know you hated them but, when they were on form, they livened up a very dull year for me. Liked their September as well

hmmm i might have to put it down to a night you hit the wine early

vocally they lived up to their spoonerism most of the time

The thing I remember about Rough Copy was the outfits - didn't they wear tartan kilts or something

But that was mild compared to Sean Miley Moor

Back on topic - I liked Luke's Play That Funky Music and Kiss From A Rose

I'm much more into Alternative Music over the Divas and Dancers over Singers acts so it would go like this.

Aiden Grimshaw - Mad World (I'm surprised nobody has said this yet)
Luke Friend - Kiss From A Rose
Luke Friend - Skinny Love
James Arthur - Impossible
Ruth Lorenzo - Purple Rain
Lauren Platt - Don't You Worry Child (a really underrated performance in my view)
Janet Devlin - Fix You
Misha B - Perfect

Out of joke act performances though I do love.

Jedward - Oops! I Did It Again
Jedward - We Will Rock You
Jedward - Under Pressure
Wagner - Creep

Ruth Lorenzo - Purple Rain
Sophie Habibis - Shelter

I think jls the way you make me feel

Alexandra Burke - Listen
Little Mix - Don't Let Go
Sophie Habibis - Shelter
Jade Ellis - White Flag
Fleur East - Uptown Funk

A few more to add:

Sophie Habibis - Teenage Dream
Luke Friend - Let Her Go
Reggie n Bollie - Shut Up and Dance/Dangerous Love

Of the novelty performances, they don't get much better than Wagner's "Viva Las Vegas" and Rylan's halloween mashup, which included Nicole's "Poison".