Magazineart.org is a free visual database of magazine cover art from the 19th and early 20th centuries. They have this to say: We like art. Art wants to be seen; it does no good if it can’t be seen. There’s a lot of art that’s been hidden away for fifty or a hundred years or more…
It’s a great resource for not only vintage illustrations, but for typography and design as well. And best of all — the images are hi-res!