Unpaywall is a new Chrome and Firefox plugin to find open access versions of articles. If you go to a journal article webpage with this installed, then it will give you a green logo on the right side of your browser if it can find an open access version; a grey logo if not.
I’ve had a bit of a try with this, and while it can’t find everything – it doesn’t seem so good at finding stuff on personal sites – it does pick up institutional repositories. I think part of the reason is that it tries to link to pieces which are legitimately online open access. One piece I tried got a green light, but the link led to a piece under embargo for another year. So, clearly not working perfectly yet, but it looks useful. Initial tests (reported in the article below) seemed to suggest half to two-thirds of articles might be available – not always clear from a publisher webpage of course. I suspect you could find a lot of these open access with a bit of internet searching, but this of course saves that time. Might it help put an end to interminable email discussion list requests for papers?
There is a fuller discussion here.