http://sci-hub.org/ or http://myescience.org/

http://reddit.com/r/scholar

https://facebook.com/groups/freepapers

https://groups.google.com/group/getarticles

https://groups.google.com/group/getarticles2

https://groups.google.com/group/slwaterflow

https://groups.google.com/group/science-liberation-front

http://thepaperbay.com/

http://articleak.allalla.com/

http://www.pirateuniversity.org/

https://en.wikipedia.org/wiki/Wikipedia:WikiProject_Resource_Exchange/Resource_Request

http://lesswrong.com/lw/eto/lesswrong_help_desk_free_paper_downloads_and_more/

http://expaper.cn/

http://aaaaarg.org/

http://www.ccapprox.info/pod/pod.php

library genesis

http://libgen.org/ http://gen.lib.rus.ec http://bookfi.org/ http://www.libgen.info/ (www is a different server from libgen.info?) http://www.libgen.net/ (this seems to have the same IP as www.libgen.info) http://vnuki.org/ http://bookos.org http://u76v7ha6j4jmtz3k2lseaso5qy36lxs77klhovmptufwcodovatq.b32.i2p/

other things worth knowing about

http://groups.google.com/group/science-liberation-front

https://github.com/kanzure/pdfparanoia

https://github.com/kanzure/paperbot