for n in range(1, 101):
      line = ""
      if n%3 == 0:
          line = line + "Fizz"
      if n%5 == 0:
          line = line + "Buzz"

      if line:
          print line
      else:
          print n


An example of FizzBuzz being written from the ground up using Test-Driven Development and Ruby: https://www.youtube.com/watch?v=CHTep2zQVAc