Take a look at
Calibre. It really is THAT good
For non-DRM'd books it is probably the easiest way to keep your collection on/off your reader. I never even loaded the Sony Reader Library onto my PC (until I went to check on something) and I do not have the Adobe software either. All of my books are DRM free and I exclusively use Calibre to track the books. I also use Windows Explorer (I guess it's=Finder for Mac) to drag and drop books as well. Calibre also allows you to change the info associated with the eBook.
Also, something I just started searching (and wish I found earlier
) is the eBooks uploaded here. The members here have taken the public domain books and have hand formatted them into, imo, a nicer cleaner read. Take a look here:
https://www.mobileread.com/forums/forumdisplay.php?f=127
Just an FYI for when you search - If you want "Tale of Two Cities" a search of "Tale Two" will return 0 records, but "Tale of Two" will show the books. So try your search a couple of different ways.
Good Luck