DGPH's Space Cadet Topo: The Day the Sun Turned Off has cute art and a pleasant story about a dashing mole, his robot companions, and their adventures in space. In tone and look, it reminded me a lot of The Octonauts, another book by Immedium Press. Indeed, like all of Immedium's books, Space Cadet Topo is an excellent option for parents tired of the repackaged cartoon episode books that fill most bookstores and Scholastic order forms. It passed the key test: My son begged me to read it again after we finished.
You can download desktop wallpapers and pages to color at the official site, and the book is $12 at Amazon.
The character (topo means "mole") is already part of a minifranchise. There's the Topo figure by adfunture available at eBay:
And Topo Joe, available at Amazon: