From the PapalEncyclicals announcement list:

“With the help of a dedicated volunteer, who has been working hard converting the encyclicals to eReader formats, the Papal Encyclicals Online now has hundreds of papal encyclicals in both MOBI and EPUB formats. So far, we have most of the available documents of the Popes from Honorious III (1216 A.D.) through Pope Leo XIII (1903 A.D.) completed.”


Scroll down to the content near the end of the page to begin seeing the eReader stuff.