I had occasion to pick my copy of Garth Nix's Lirael off my shelf the other day (the occasion being merely that I like to pick up really good books). My copy is a galley/ARC that has the Leo & Diane Dillon art on the cover. And even though I've read this story eleventy times and looked at the cover way more than that, not until last night did it occur to me that L&DD might have been slyly telegraphing one aspect of Lirael's fate in the picture. It's not a spoiler--I'm not even sure it's intentional--but, damn, now that I see it, it seems so obvious. And I love it. (If you have read this book, you should see what I mean. If you haven't read it, shame on you. Get thee to a bookstore/library stat!)
In the US, later printings of the Abhorsen series shifted from the amazing Dillon art to more abstract covers with "charter mark" style symbols. Personally, I never dug those covers, though it never stopped me from rec'ing the books to all and sundry when I worked in the bookstore. The release of Clariel reminded me of the series as a whole, and I really cannot praise it highly enough. It's up with His Dark Materials and The Dark is Rising for children's lit that I'd pack for the apocalypse.