Title said it all like the top 3 of:

Gaga
Rihanna
Beyonce
Shakira
Adele
Avril
Legend X
Kelly Clarkson
Lana
Madonna
Mariah
Azealia
Lorde

ETC...

And te other ones who comes to your mind

Where is the Little Pokemonsters tho

This could take a while...

Where is Cher tho

Where is KATY tho

Ones that come to mind for me..

Gaga - Jolie's Lips
Rihanna - liberalmusiclover
Beyonce - DG1
Shakira - Pedro
Adele - Ichinaru19
Avril - emmanual93
Legend X - DMF
Kelly Clarkson - Mhs90
Lana - I don't know
Madonna - DitaBoy12
Mariah - Daydream
Azealia - Jameson something
Lorde - SaveMeOprah

Gaga: Jolies lips
Rihanna: Edgeofaddiction
Legend X DMF
Madonna Ditaboy12
Lorde save me Oprah
Kesha Ks- Dollar

Gaga-H-I-M, Harujuku, GoneHome Slay flawless little monsters
Rihanna-liberalmusiclover
Adele- me, me and me
Avril-Not sure since half the time time the Avril stans are fighting or shading Avril
Kelly Clarkson-ClinicStudent KCLA and some others
Lana-LanaDelRey
Lorde-SaveMeOprah
Katy: umich

Katy - umichgrad
Lorde - Save Me Oprah
Ke$ha - Ks Dollar
Miley - Miley Cyrus
Gaga - Jolies lips
Taylor - OnlyManInTheWorld (or smthg like that)

Can't think of more

Cher: citrus
Shakira: Shakira stan
Katy: umichigrad
Adele: That Adele stan inachuru
Avril Emmanuel punk
Britney:

The spelling though

Gaga: Jolie's Lips
Katy: H-I-M
Adele: XD
Taylor: Only Man In The World
Rihanna: rihannafan
Britney: Duca / Katie but toysoldier is coming for wigs
Lorde: Save Me Oprah
Kesha: Vin

Where is Carly?

Adam Lambert: Glam + Rem
Lea Michele: Rem (for now until you gorls all start hopping on the bandwagon when Cannonball releases tomorrow - preview here)
Jason Derulo: Sinister/White Tigers/castro + Rem
Glee + Glee Cast: Rem
Karmin: Rem
Icona Pop: Rem
Cee-Lo Green: Rem