Someone

SELECT s.id, pop.cnt 
  FROM news_stories s, news_stories_sites ss, 
  (
  SELECT object_id, count(object_id) as cnt
  FROM mostpopular_mostpopularhits
    where content_type_id = 61
    AND click_date BETWEEN '2008-04-15 15:00:00.685806' AND '2008-04-16 16:00:00.685833'
     group by content_type_id, object_id
     ) pop
     WHERE pop.object_id = s.id
      AND s.id = ss.story_id
      AND s.status = 1
      AND s.pub_date <= NOW()
      AND ss.site_id = 1   
    ORDER BY pop.cnt DESC
    LIMIT 50 ;
-----------------
EXPLAIN
-----------------
 Limit  (cost=7539.07..7539.19 rows=50 width=12)
   ->  Sort  (cost=7539.07..7539.76 rows=276 width=12)
         Sort Key: pop.cnt
         ->  Hash Join  (cost=6738.60..7527.88 rows=276 width=12)
               Hash Cond: (ss.story_id = s.id)
               ->  Seq Scan on news_stories_sites ss  (cost=0.00..656.25 rows=34740 width=4)
                     Filter: (site_id = 1)
               ->  Hash  (cost=6735.15..6735.15 rows=276 width=16)
                     ->  Nested Loop  (cost=4773.44..6735.15 rows=276 width=16)
                           ->  HashAggregate  (cost=4773.44..4778.13 rows=375 width=8)
                                 ->  Seq Scan on mostpopular_mostpopularhits  (cost=0.00..4713.34 rows=8014 width=8)
                                       Filter: ((content_type_id = 61) AND (click_date >= '2008-04-15 15:00:00.685806+10'::timestamp with time zone) AND (click_date <= '2008-04-16 16:00:00.685833+10'::timestamp with time zone))
                           ->  Index Scan using news_stories_pkey on news_stories s  (cost=0.00..5.20 rows=1 width=4)
                                 Index Cond: (pop.object_id = s.id)
                                 Filter: ((status = 1) AND (pub_date <= now()))
(15 rows)

----------------------------
EXPLAIN ANALYZE
----------------------------
 Limit  (cost=7539.07..7539.19 rows=50 width=12) (actual time=295.352..295.582 rows=50 loops=1)
   ->  Sort  (cost=7539.07..7539.76 rows=276 width=12) (actual time=295.348..295.417 rows=50 loops=1)
         Sort Key: pop.cnt
         ->  Hash Join  (cost=6738.60..7527.88 rows=276 width=12) (actual time=164.690..288.492 rows=3510 loops=1)
               Hash Cond: (ss.story_id = s.id)
               ->  Seq Scan on news_stories_sites ss  (cost=0.00..656.25 rows=34740 width=4) (actual time=0.060..60.333 rows=34740 loops=1)
                     Filter: (site_id = 1)
               ->  Hash  (cost=6735.15..6735.15 rows=276 width=16) (actual time=163.103..163.103 rows=3510 loops=1)
                     ->  Nested Loop  (cost=4773.44..6735.15 rows=276 width=16) (actual time=83.310..155.054 rows=3510 loops=1)
                           ->  HashAggregate  (cost=4773.44..4778.13 rows=375 width=8) (actual time=83.177..90.455 rows=3512 loops=1)
                                 ->  Seq Scan on mostpopular_mostpopularhits  (cost=0.00..4713.34 rows=8014 width=8) (actual time=0.051..65.881 rows=7886 loops=1)
                                       Filter: ((content_type_id = 61) AND (click_date >= '2008-04-15 15:00:00.685806+10'::timestamp with time zone) AND (click_date <= '2008-04-16 16:00:00.685833+10'::timestamp with time zone))
                           ->  Index Scan using news_stories_pkey on news_stories s  (cost=0.00..5.20 rows=1 width=4) (actual time=0.010..0.012 rows=1 loops=3512)
                                 Index Cond: (pop.object_id = s.id)
                                 Filter: ((status = 1) AND (pub_date <= now()))
 Total runtime: 296.042 ms
(16 rows)