http://www.perlmonks.org?node_id=521141

Just came across this one:
#!/usr/bin/perl sub __{$_[0]=~y-=#&!~_`'.+,/<>():;?- .,eintsrahgldmfopv-;print@_} sub _{($,,$:)=split/=/,$_[0],2;$* =$*?"$:$*":$:;__ "O_=`,!=$,=>+y=:)=C,r~'`(+'=(y=`.u!=<:?!=/+?!=`:=(!$/$*#$/$/"}map{_$_ }")~.'`=+=;+.`.~>/!=~_=+=;!+.=`.!!","'!c:_>=`w:=`u.`<!=>:?!'=+_>=" ,"`,~.>=`,.!!=).!_c,=,!_'&=","):u.`,=):u.=c+<<~_/=b~.>'&$/" ,")~)`,=)~?!=/:<>!_=.~_/'&=","'~x`,='~x=/!!'!=+-<+y~_/&=" ,"'!?!_`,='!?!_='w+_'=+-'w~((~_/&$/","!~/,`,=!~/,`=(+~> '=+-(~<k~_/&=" ,"_~_`,=_~_!=<+>~!'=>+_c~_/&=","`!_`,=`!_=<:.>'=+-<!+;~_/&$/" ,"!<!?!_`,=!<!?!_=;~;!.'=;~;~_/&=","`w!<)`,=`w!<?!=>.u((!.'=>.u((~_/&=
What it does is nothing but generate the following poem :
On the first day of Christmas my true love gave to me a partridge in a pear tree. On the second day of Christmas my true love gave to me two turtle doves and a partridge in a pear tree. On the third day of Christmas my true love gave to me three french hens, two turtle doves and a partridge in a pear tree. On the fourth day of Christmas my true love gave to me four calling birds, three french hens, two turtle doves and a partridge in a pear tree. On the fifth day of Christmas my true love gave to me five golden rings, four calling birds, three french hens, two turtle doves and a partridge in a pear tree. On the sixth day of Christmas my true love gave to me six geese a-laying, five golden rings, four calling birds, three french hens, two turtle doves and a partridge in a pear tree. On the seventh day of Christmas my true love gave to me seven swans a-swimming, six geese a-laying, five golden rings, four calling birds, three french hens, two turtle doves and a partridge in a pear tree. On the eighth day of Christmas my true love gave to me eight maid s a-milking, seven swans a-swimming, six geese a-laying, five golden rings, four calling birds, three french hens, two turtle doves and a partridge in a pear tree. On the ninth day of Christmas my true love gave to me nine ladies dancing, eight maid s a-milking, seven swans a-swimming, six geese a-laying, five golden rings, four calling birds, three french hens, two turtle doves and a partridge in a pear tree. On the tenth day of Christmas my true love gave to me ten lords a-leaping, nine ladies dancing, eight maid s a-milking, seven swans a-swimming, six geese a-laying, five golden rings, four calling birds, three french hens, two turtle doves and a partridge in a pear tree. On the eleventh day of Christmas my true love gave to me eleven pipers piping, ten lords a-leaping, nine ladies dancing, eight maid s a-milking, seven swans a-swimming, six geese a-laying, five golden rings, four calling birds, three french hens, two turtle doves and a partridge in a pear tree. On the twelfth day of Christmas my true love gave to me twelve drummers drumming, eleven pipers piping, ten lords a-leaping, nine ladies dancing, eight maid s a-milking, seven swans a-swimming, six geese a-laying, five golden rings, four calling birds, three french hens, two turtle doves and a partridge in a pear tree.
cheers!