Kobo has launched 250+ Vox-only books in their bookstore:
http://www.kobobooks.com/browse/Just...28voxcontentCA.
These include mostly children's books and also comics, like Archie, Rising Stars, and Artifacts. About 10-15 are free books, about half of them comic books.
The comic books are beautiful on the Vox screen, although often you have to pinch-zoom to read the captions (admittedly zoom & pan is effortless on the Vox).
Two books I downloaded say "A format compatible with your reader isn't available yet", which I presume means we'll need the next Vox system update to read these.