I really like the ones that have felt flaps from nosy crow "where's the...l and that "that's not my..." books.
He's 9 months now and really likes those.
He's got an older brother but he only started being interested in books from 2 1/2, so we now have loads of books for him but I didn't bother buying too many when he was younger as there was naturally not much interest, early mover and very busy at the time, never sat still or on my lap but my second boy already loves them and is so different (I actually love it).
Any more suggestions as in titles and what yours loves/ loved? X