I keep 'em all on my Kindle.

(And keep my calibre library backed up on a portable hd, too.)
I have every book in at least one collection, so with my home page set to display "Collections" it is not difficult to find what I want somewhere in my 10 or 12 collections. The main ones, btw, are "Reading Now," "Unread," "Fiction," and "Nonfiction."