"Why Our Drug Laws Failed and What We Can Do About It" by. Judge James P. Gray
"The Emperor Wears No Clothes" by Jack Herer
those are just two off the top of my head. just from looking at the related products on amazon for those books, i can see there are at least five that you can use for your paper
i haven't read the latter, but the first one i did read for the class i took on drug law. its full of facts about how much money we waste sending non-violent drug criminals (a.k.a. for possession) to prison, how real (violent) criminals are being released so that drug users can serve mandatory sentences, and other various damages to our society. also has a few different propositions on how this can be fixed.