#!/usr/bin/perl -w
use strict;
use Data::Dumper;

my @array = (
    { a => 1, b => 2, c => 3},
    { b => 1, d => 2, c => 3},
    { a => 1, b => 2, c => 3},
    { a => 2, b => 2, c => 3},
    { a => 2, b => 1, c => 3},
);

my %count;
my @unique;

    # eats away at @array, use for() if you want to keep it
while (my $entry = shift @array) { 

    # need to sort by something because an equivalent hash migh
    # return the key/value pairs in a different order
    my @sorted = map { $_, $entry->{$_} } sort keys %$entry;

    # create a unique string and see if we've seen it before
    next if $count{ join"#",@sorted }++;

    push @unique,$entry;
}
print Dumper(\@unique);
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I'm not so sure how efficient this is with your data, though. Try it out. :-)

by the way: if your hashes are really the same objects (i.e. references to the same structure) you can just compare the stringified reference (ie. $href eq $href2). But considering your question, you're probably not in that situation.