What you need is a priority queue, such as the Fibonacci heap.

For perl, there is Array::Heap, which ought to perform adequately.
This following does 1M counts + 1000 toplists in a second or two.
(Update: performance comparisons with a database are welcome.)

#! /usr/bin/perl -l

use Array::Heap;
print "starting";

my @h = map [-rand, "item $_"], 'aa000' .. 'zz999';
print int(@h), " elements";
make_heap @h;
print "heap made";

sub hits { --$h[$_][0], adjust_heap @h,$_ for @_; }
sub batch { hits map {int @h*rand()**4} 1..$_[0]; }

sub rotate {
  $_->[0] *= rand, $_->[1] .= '.',
    push_heap @h,$_ for map {pop_heap @h} 1..$_[0];
}
sub top {
  map sprintf("%8d  %s", -$_->[0], $_->[1]),
    map {push_heap @h,$_;$_} map {pop_heap @h} 1..$_[0];
}

for (;;) { 
  batch(1000), top(10) for 1..1000;
  print for "", top(10);
  rotate(3);
}
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