• <code> tags: learn them, live them, love them.
• perldoc -q "sort a hash"
• Fish:

  my @by_stud = map { my $t = $scores{$_};
                     [sort { $t->{$b} <=> $t->{$a} } keys %{$t}] }
                       keys %scores;
  [download]

Update: Actually, I just checked perldoc perldsc and it gives almost an exact example of sorting a similar HoH. Search for Access and Printing of a HASH OF HASHES.