DS enjoyed the Bunnicula books (One of the titles is The Celery Stalks at Midnight). We also liked Trouble in Bugland (a spoof of Sherlock Holmes). Even though it is pretty easy, no one in our family has tired of Captain Underpants because they are very clever. In the last few years, DS has really enjoyed books by Terry Pratchett--I haven't read them, but he says they are very funny.