Well here's my list, based on different music styles I've listened to during my life:
1) ABBA - Arrival: Abba's most known album, it's perfect to dance and feel happy!
2) Natalie Imbruglia - Left of the middle: This was the album that included her most known song, Torn. I still listen it with nostalgia.
3) Lady Gaga - The Fame Monster: Gaga's first album, surprising as her with her style.
4) Mecano - Descanso dominical: One of Mecano's most known albums including some of their top hits.
5) Silvia Pérez-Cruz - 11 de novembre: an intimate album to listen on rainy dais.
6) Carla Bruni - Quelqu'n m'a dit: Bruni's first album, with her voice and guitar, it's an album perfect to stay at home on a quiet afternoon.
7) The Corrs - Forgiven not forgotten: Before they became commercial and sound equal in all their songs, The Corrs first album was something fresh when it was launched.
8) SIA - Some people have real problems: Sia used to write famous song for pop starts, but never sang them. One of her first albums was this fresh proposal.
9) Adele - 19: At her 19, Adele launched her first work exposing her great voice to the world.
10) Christina Aguilera - Stripped: Despite it is a pop-album, and probably it wasn't considered at that time as a perfect composition, it was an album organizaed in chapters, full of interludes connecting all songs.