The BBC's Planet Earth series is fantastic. Reminds me of Shakespeare: "There are more things in heaven and earth then are dreamt of your in philosophy"... Makes you really appreciate the beauty on this planet.

Also - a bit of a curveball answer: I really like Documentary Now! (on Netflix). They are parodies of really well known documentaries. So I ended up watching the parody and then looking for the source material on which it was based. I realized that my wife (art major) knew almost all the original documentaries and I knew almost none (engineer...)

EDIT: Wikipedia has the mapping of parody->original : https://en.wikipedia.org/wiki/Documentary_Now!