[dspoka]

Some people have already mentioned these but so far I'm using:

Karpathy's http://www.arxiv-sanity.com/library subscribe to archive email lists

Semantic Scholar (no notifications) is good for manually finding things

Google Scholar notifies you when your papers get citations... Unfortunately they don't have a way for you to get notified if the paper is not yours.. so I made a few fake accounts that add papers to the library as if they are the author and then I set up a forwarding to my email. (really wish they would just expand the notified of citations feature to your library and not just your papers but whatever)