This is a linkpost for http://unpaywall.org/
This is a plug in for Chrome browser right now, Firefox port is coming.
" Millions of researchers are currently uploading their own fulltext PDFs to preprint servers and institutional repositories worldwide, making them free for anyone to read. But there was no easy way to find them as we browsed. So we made one! Eventually, we hope tools like Unpaywall will nurture the transition to fully open access scholarly publishing, by closing the gap between readers and freely-available fulltext.
…
We gather content from thousands of open-access repositories worldwide. To help us, we rely on some fantastic open data services, especially PubMed Central, the DOAJ, Crossref (particulary their license info), DataCite, and BASE. "
The obvious next step seems to be a fork of this extension that doesn't restrict itself to legal sources. That would make it a hell of a lot more useful.
Preprinting is becoming much more common, as NIH and others are allowing it in grant requests, so there will be a lot more available.
It would also be a nice addition to add the scientists own blogs to the search algo, as they are allowed to post to private blogs, just not the academic site that they are aligned with, sometimes.
Looks like source will be available, so could add any sites you want.