I can't really choose one, but a few album nominations I'd have are possibly the following:
Chromeo's Fancy Footwork: great fun electronica disco sound, and great stuff to just stick on and get your feet tapping.
Pink Floyd's Dark Side Of The Moon: obvious reasons - subtle references to the meaning behind the album, great sound, and just easy to relax to, imo.
Bloc Party's Intimacy: funky hardcore electro sound which you can dive into straight away if you enjoy a bit of industrial sound - can't really comment on the meanings behind the track listing or anything like that, though, as I'm usually carried away by the beats.
Flobots' Fight With Tools: best rap albvum I have as it explores American corruption and everything wrong with the country. The use of violins, horns, guitars and vocals are very effective, as well. It blows the rap stereotypes out of the water, too; definitely worth listening to.
As again, there are loads more, but those are just a handful of what I'd call great albums.