<i>Hail to the Thief</i>, by Radiohead.
I know everyone says <i>Kid A</i> is their best album (except for this crazy friend of mine who thinks it's <i>Pablo Honey</i> but she's crazy) but I've sinned and haven't heard the whole thing. Still, I bet even after I have, <i>Hail to the Thief</i> will be my favourite. I love every single one of the songs (which is rare for me), the lyrics, the alternate titles; I even love the album art.

Except for a handful of others, there are very few albums out there where I can actually listen to the whole of it without skipping a song, let alone loving the whole thing.