The #1 slot is a tie, between:
- Yuri Gagarin's flight aboard Vostok 1 - the first human foray into space
and
- Apollo 11 - the first human contact with another heavenly body
After that, comes the
Mars Exploration Rover-2003 mission, which launches two rovers to Mars in May and June of this year (this one makes the list because it is my mission!)
-dave