Do look at our book upload section (-- click on
ebooks on the blue bar near the top of this page). You will find a load of classics specially formatted lovingly by hand for the Reader. Choose the ones in LRF format. They will look so much better than most PDFs.
You can also get free classics in LRF from Manybooks and Munsey's.
And Feedbooks has PDFs which are specially sized for the Reader, so that you don't get eyestrain.
Here's a link to our wiki page on free books:
https://wiki.mobileread.com/wiki/Free_eBooks
(There's also a link to our wiki at the very top of this page.)