I think your list would have to include "We Shall Overcome" Pete Seeger. I would leave "This Land Is Your Land" off because it is from earlier than the 60s. "Blowing in the Wind" by Dylan could be another one.

Another question to ask in formulating the list is do you mean most influential--like the two I suggested--or best in sound/lyrics?

I will think about this and come up with more later!

Michele C.