In no particular order:
Male porn star - no explanation necessary
Helicopter Pilot/other aviator - gobs of time to yourself enjoying nature's beauty from above
CIA spook - the sheer adventure of it all
Midwife/Doctor who delivers babies - how much more fulfillment can there be than to bring in a new life into the World
Astronomer/astrophysicist - you can come up with just about any wacky theory to explain the Universe and no one on this Earth can prove you wrong