Didn't you mean to make this a grep? :)

my @files = grep s/\.ram$//i , readdir DH;
[download]

Also, I agree with dws regarding the readability of the character classes, and believe you're altogether mistaken regarding the performance issue:

use strict;
use Benchmark qw(cmpthese);

my $strorig = 'yabadabadooo this bud is a buda fora youa';

cmpthese (-3, {
  mod   => sub { my $str = $strorig; $str =~ m/.*BUD.*/i },
  class => sub { my $str = $strorig; $str =~ m/.*[Bb][Uu][Dd].*/ },
});

## Results (under ActiveState 5.6) ##

          Rate class   mod
class 347719/s    --  -15%
mod   408606/s   18%    --
[download]

   MeowChow                                   
               s aamecha.s a..a\u$&owag.print