I'm not sure if our team has had any of the major, life-shaping achievements that Dave had in his post yet - we're only four years old, so the freshmen that joined in our first year are still on the team, albiet only for one more competition.
In that first year, we won the Rookie All Star at Great Lakes, Western Michigan, and Nationals. I joined the team in the next year, so I wasn't able to experience that, but those are all proud moments.
The best moment that I've seen in my three years on the team came last year, at Palmetto. Team 507 arrived at the competition with a chassis, no programming, two adult mentors, and a handful of students. We spent the competition with them, helping them to finish their robot and becoming friends in the process. They even beat our robot in one of their matches against us.
That would have been enough for me, but we won the Sportsmanship award because of our time with 507.