I've been getting into this as a way of keeping up with new papers before they hit the journals.
Here's one that seems to be hidden on the NBER website:
http://www.nber.org/rss/newpol.xml - new NBER papers in political economics.
I mentioned REPEC already. SSRN's feeds for individuals don't seem to work. Most individual journals also have RSS feeds and some have feeds for pre-published papers.