My solution: 63 characters without the quotes, or 60 characters with them.

1.upto(100){|i|i%3==0&&x="Fizz";i%5==0&&x="#{x}Buzz";puts x||i}

1.upto(100){|i|i%3==0&&x="Fizz";i%5==0&&x="#{x}Buzz";p x||i}