The Digital Comic Museum offers free access to hundreds of pre-1959 comic books, uploaded by users who often offer historical research and commentary alongside high-quality scans.
The site’s moderators and administrators are particularly careful to avoid posting non-public-domain comics (a complicated designation, as described in this forum thread). The resulting archive is devoid of many familiar comic-book characters, like those from Marvel, D.C., or Disney.
On the other hand, because of this restriction, the archive offers an interesting window into the themes of lesser-known comics in the Golden Age—romance, Westerns, combat, crime, supernatural and horror. The covers of the romance comics are great examples of popular art.
An interesting link found among my daily reading