I'll add my solutions to the thundering horde. My first solution was
moderately clever:

puts
(1..100).map{|n|[[3,'fizz'],[5,'buzz']].inject(n){|s,a|s.is_a?(Fixnum)?s
=a[1]:s+=a[1] if n%a[0]==0;s}}

then I tried to use as few characters as possible:

puts (1..100).map{|n|n%15==0?:fizzbuzz:n%5==0?:buzz:n%3==0?:fizz:n}
puts (1..100).map{|n|n%15>0?n%5>0?n%3>0?n:'fizz':'buzz':'fizzbuzz'} 

- donald