Here's an example using HTML::TokeParser

#!/usr/bin/perl -w

use strict;
use HTML::TokeParser;

# Regex representing the list of acceptable tags
my $ok_stuff = qr/^(p|br|h.|font|pre)$/;

# Some test html.
my $html = "<p><br><h3><a href='evil.js'>Testing</a></h3></p>\n";

# Instantiate the TokeParser
my $parser = new HTML::TokeParser (\$html);

# Loop until all tokens are read
while (my $token = $parser->get_token())
{
        # Immediately print any "text" token
        if ($token->[0] eq "T")
        {
                print $token->[1];
        }
        # Check all other tokens against the regex before printing
        elsif ($token->[1] =~ $ok_stuff)
        {
                print $token->[$#{$token}];
        }
}
[download]

The above code prints out "<p><br><h3>Testing</h3></p>"

-Matt