You can always find the working links on Wikipedia.

https://en.wikipedia.org/wiki/Sci-Hub

I use the chrome plugin. This plugin looks bad but is actually pretty sick. One certain pages it will replace the DOI with the sci-hub link.

Dont forget Library Genesis too! http://gen.lib.rus.ec/

http://sci-hub.hk still works fine for me.

https://sci-hub.tw/ works for me.