Here's a list of some good leftist books I've come across over the years. Click on the titles for the PDFs. It's a somewhat arbitrary list, but I tried to keep it confined to fairly easy-to-read books, not overly theoretical or abstruse ones that might leave the beginning reader bewildered. I've been unable to find PDFs of certain excellent works, unfortunately. You can also consult the Marxists.org website, a treasure trove. Or check out the extraordinary footnotes to Chomsky's Understanding Power, which have informative excerpts from hundreds of books.