nov 26, 2001 - Curiosity
NASA sends a rover out to space to go to Mars, the first of it's kind. It was created to go to Mars, and roughly 9 months later (August 2012) has landed. It is scheduled to serve as the basis for the rover "Mars 2020" which is far more advanced, and will give us a better analysis than Curiosity did. This shows that NASA and SpaceX are the 2 leading competitors in Space Exploration and each on is now competing to land a man on Mars.
Added to timeline:
Space Exploration Timeline
Important Dates in Space Exploration