As a child I worked my way through pretty much every book in the local library that had a Puffin on the spine; more often than not it was a very good book. Certainly bringing Tove Jansson's Moomin books into English and keeping them in print is justification enough for Penguin's children's imprint to be toasted to the heavens.
Puffin have now launched a new series of Puffin Classics, modelled on the Penguin Classics. They're a great series of books, very attractively designed. Each has a very appealing illustration on the cover (usually with part of it protruding over the white band, making them more childishly anarchic than the adult classics) and bold, limited colour schemes that catch the eye. Click for much bigger versions.
I'm not sure whis responsible for most of these illustrations, although the Alice in Wonderland cover must be by the man who wrote the introduction, Chris Riddell (a children's writer who I know better through his great covers and cartoons for the Literary Review magazine). The cover for A Little Princess looks a lot like Vania Zouravliov's work, but I may be wrong.
(UPDATE: Indeed, I'm completely wrong--an anonymous commentor informs me that A Little Princess's cover is the work of Kate Willis-Crowley.)
Penguin India have also got in on the act, releasing three Indian children's classics as part of this series. The covers are mostly photographic rather than illustrative, but they are also very nice-looking books. I've got hold of a copy of Making a Mango Whistle, which looks very interesting.
My only objection would be that for the non-Indian titles, the authors of the introductions get bigger billing than the authors of the books, which seems a bit rough.