My son is just coming up to the age when he can start occupying himself with books etc, and doesn't always need you to read to him anymore. I first got him the Where's Wally books, which he loved and this is now my latest acquisition. After buying this one though, I have now got the whole set: Puzzle Master Collection - 6 Books, RRP £41.94 (Puzzle Master)
(It worked out cheaper buying the whole set, even if I already had this one, rather than buying them individually) and he absolutely loves them!
He's 6, so can work his way through the text himself, and it keeps him busy for hours, but they also work really well if you want to read them together and work your way towards the end, using the clues on each page.
One or two of these books are defenitely going top on the packing list for our holiday this summer, will be invaluable for all the travelling time!