Huh, I realized that the things that I play over and over are playlists rather than albums, especially in the last five years. Some of the stuff that I've kept on loop or had in my car for a long time:
A playlist of Jason Mraz's songs, mostly live recordings that I ripped from Youtube. I think most of the tracks I ripped aren't even on an album.
American Idiot - Green Day + a playlist of other Green Day songs from other albums
Soundtrack to Les Choristes + some other songs that the main soloist, Jean-Baptiste Maunier, also performed. Actually, it was part of a playlist of my favorite French music that I would also play repeatedly.
Romance of the Violin - Joshua Bell
Greatest Hits - Itzhak Perlman (had Carmen, Introduction and Rondo Capriccioso, Symphonie Espagnole, etc. on it)
And this might be a little unexpected, but...I effing love the band Hanson. I actually didn't become a big fan until their third album Underneath, which is one of my favorite albums of all time. I was probably rotating through four different Hanson albums in my car at one point.
Playlist of Adam Lambert tracks. His new album Trespassing is actually what I've been playing over and over for the last two weeks now. I think it'll be an album that I repeat for a long time.
Lungs - Florence + The Machine
Playlist of Kanye West tracks, mostly from Graduation and My Beautiful, Dark Twisted Fantasy
The Fame - Lady Gaga
Playlist of Adele tracks