If you're into Nature documentaries, anything by David Attenborough. He's kind of regarded as national treasure in the UK, and given the understated quality of most of his documentaries, it's well deserved.
Planet Earth is probably the broadest in scope, but the various 'Life of' series go into more detail.
There are clips on youtube if you want to 'try before you buy'.
Edit; for space stuff; 'From the Earth to the Moon', 'The Right Stuff (1983)', 'Apollo 13'.
Military stuff wasn't specifically mentioned in your OP, but 'Band of Brothers' is one of the best war dramatisations ever made, and it's sequel 'The Pacific' is also well regarded.