I own all albums of: Britney, Katy, Rihanna, Lana, P!nk and almost Christina. I will buy Lotus when it only costs 5 Euro.
Britney is the only artist I own also every physical single, DVD, remix albums, GH, Single Collection, Pepsi CDs etc.

Alicia Keys, John Mayer, Jason Mraz and No Doubt

Rihanna will soon be added to the list. As soon as I can get my hands on MOTS

exactly

Lady Gaga
Beyoncé
Britney Spears
Madonna (I'm almost done, I think I have like four albums left)
Azealia Banks
Jonsí
Janelle Monáe
Zedd
Adam Lambert
Fergie
Florence + The Machine
Imagine Dragons
The All-American Rejects

Yeah, I know that some of these have short discographies

Demi, Gaga, Jessie J, Rihanna, Amy Winehouse.

I'm trying to get Xtina's tho

Too many to name...

Just Coldplay, Gwen Stefani (the two solo albums), Bruno Mars, Lily Allen and Lana del Rey (both versions), but I wish I had Gaga's, The Killers', Adele's and many more.

Rihanna, Mariah Carey, Xtina, Nicki & Ke$ha

Yes for nicki!!!

Michael Jackson
Janet Jackson
Madonna

Yes, I have their remix albums, their greatest hits, their compilations, their DVD releases, all of it.

I own most of Beyonce's records. I'm just missing the extended plays.

I have all of Kanye West's, except Cruel Summer.

I have almost all the Kings of Leon records, except their EP's.

I'm close with Mariah Carey and Marvin Gaye.

I own physical copies of every studio album from Shania Twain, Taylor Swift, Faith Hill and Lady Antebellum (and Carrie Underwood?).

I also own the studio albums of Florence + The Machine, Lady Gaga and Ellie Goulding as digital copies.

No Doubt.

PCD/Nicole Scherzinger
Evanescence
Bruno Mars
Gwen Stefani
Justin Timberlake
Lana Del Rey
Linkin Park
Black Eyed Peas (the albums since Fergie, I don't own any without Fergie)
Fergie (have her standard and re-release)
Ke$ha (all studio albums, not her remix)
and I have all regular Christina albums, just don't own her Spanish and Xmas album

I have all of Ke$ha's (including I Am The Dance Commander) , Christina Aguilera's, Lana's , and I just need the Re-Up from Nicki Minaj's

Billy Talent
Ellie Goulding
Florence + the Machine
Lady Gaga
Lily Allen
Loreen

There are more I care about enough to own their entire discographies, just haven't gotten around to buying yet.

Lady gaga, Mariah, beyonce. Alicia keys, Katy perry, Kesha, nicki Minaj, almost Rihanna almost BEP almost Adele